The tic-tic-tachs are not very accurate. Are you feeling all 3 gears? With 2.56 gears the car should glide down the toad at barely more than a fast idle. My guess is either the speedo, tach, or both are way off.

Make a couple ful throttle acceleration tests, make sure you don’t over rev the engine. See if it will eventually go into 3rd. Next, at about 20-25mph, drop the shifter into 1st gear, does it go back to 1st and have engine braking (meaning the engine is slowing down the car without the use of the brakes) If you have engine braking in manual 1st gear, and a solid engagement into reverse, you can be reasonable sure the clutches are in decent shape. In 3rd gear the direct clutches mechanically lock the gearset together for direct drive. The direct clutches also become the driving clutch in reverse gear. The low/reverse clutches apply in manual 1 gear to provide engine braking, the also engage for reverse gear. If everything checks out so far, you can be reasonably sure your trouble is valve body related. Before dropping the pan and drenching your hair in nasty ATF, carefully inspect the vacuum hose to the modulator. If it’s rubber hose, or kinked steel tubing, replace it with the proper steel tubing. Make sure you have a good vacuum supply, sometimes the fitting on the intake gets gummed up with carbon. Just because you have vacuum at the hose, doesn’t mean you have a STRONG vacuum signal. If everything checks out, make sure the lockdown cable under the dash is adjusted right. The cable should be pulled right at about the same time the gas pedal is at WOT. Make sure the cable hasn’t been kinked , melted, twisted, and moves and returns to idle freely. If all checks out at this point, replace the modulator. It’s about 10 bucks at AutoZone, and it has a small screw in the vaccum neck to fine tune shift points. Spray the bolt that holds the modulator to the case with lots of penetration oil, and I would strongly suggest heating the case with a torch where the bolt threads in. The bolt is sometimes held in place with “environmental Locktite” and can break off in the case. If the bolt does break, repair clips are available that use a pan bolt to retain the modulator.

After all this and you still have no 3rd gear, it’s time to drop the valve body. I would suggest installing a TransGo or B&M shift kit at the same time, the kit will have instructions and include durability upgrades. A shift kit on a TH350 is pretty easy, just make sure to clean everything and use Vasoline (not wheel bearing grease!) to retain the little check ***** in the case. It helps to refrigerate the Vaseline so it isn’t as runny to hold the ***** in place.

My bet is a vacuum supply issue or a bad modulator. A part throttle 1-2 shift at 18mph seems a little high. Hopefully it’s a easy fix.

i had a machine down at work last night, I had lots of time to kill. 😎

Your vacuum is good, at least good enough that the trans should shift normally. Did you try a WOT run to see if it would eventually go into 3rd? Is the kinda clfown canle free to move? If you pull the cable, does it snap back freely?

If the 1-2 shift is normal most likely the governor is fine. The kick down cable goes thru the firewall and connects to the throttle pedal. On the transmission it comes out of the case near the cooler lines. Or if the trans/engine has been swapped it may be on the carburetor linkage. Either way if the cable is holding the detent valve in its WOT position it’s not going to shift until maybe 60-70mph.

The cable travel should max out at WOT. If you pull the cable tight does it snap back when release it?

I have been building transmissions for about 20 years, I have heard all the wives tales about not changing fluid because it stirs up crap and causes issues. My opinion, that’s a bunch of crap. If the transmission is serviced on a somewhat reasonable basis, there shouldn’t be a bunch of crud to get stirred up. Secondly, would you never change your engine oil and filter? Of course not. Third, if the trans fails after a service, it was already on its last miles. Let’s face it, most people don’t bother changing fluid until they have a concern.

My Dodge Ram diesel has 180K of hard miles, lots of towing, heavy loads, and is still going strong. I installed a TransGo shift kit at 40000, and change the fluid l,filter and adjust the bands about every 25000. There is never more than a light dusting of crud in the pan, nothing more than normal clutch and band wear. I suggest to anyone who will listen there is nothing wrong with regular transmission maintenance.

TransGo, B&M, TCI, Superior, all make excellent shift kits. If you install one with the Towing calibration you will have a slightly firmer and quicker shift, that won’t knock the dash out of the car. The street performance calibration will be pretty hard bang/screech shift at full throttle. All the shift kits basically work the same, the Superior and TransGo kits are a little more “civilized” for daily driving. If you have a slightly looser converter, install the B&M kit, it’s cheaper and the looser converter will absorb a lot of the harshness.

Shift kits in TH350 are pretty easy to install. Between the instructions and YouTube videos are all the help you need. If your trans doesn’t have a drain plug, buy a drain plug kit and big drain pan. Drill a hole in the pan where you want the drain plug, let the fluid slowly drain into the pan. Follow the shift kit instructions, keep everything CLEAN and organized. Use vasoline to hold the check ***** and small parts in place. Make sure all the valves move freely, make sure the kick down cable inside the trans is free to move. Good luck

Take it out for a highway drive, if it hasn’t gone into 3rd gear by 4000 rpm chances are it’s not going to. Find a empty quiet stretch of road to really wind it out, don’t over-rev it but get it up to a speed that there is no question it should have gone into 3rd.

I just thought of something, surely you checked the shifter linkage to make sure drive on the PRND2L is actually 3rd gear on the transmission?