I did an engine swap. Took out the 350 and replaced it with a 455. My question is. Is there a 5 or 6 speed automatic transmission out there that I could be installed without having to cut out the tunnel?

 

You can get a 2004R with a BOP transmission pattern that will fit your 455. It would definitely have to be upgraded to withstand the torque. A 700R4 or 4L60E swap can also be done. I don't know about a 5 or 6 speed automatic.

 

No. There is a FOUR speed AT that bolts up and fits easily, the 200-4R as noted. It requires internal mods to survive behind a 455. The 4L80E also fits with very minor tunnel massaging, but it requires an adapter plate. The 4L80E actually fits better than the 700R4/4L60E and is significantly stronger. The five and six speed ATs are huge, heavy, and do you really need TWO overdrive ratios? The only reason these transmissions have so many gears is to keep the engine in the most optimum RPM band for a couple of extra MPG on the CAFE test. Having driven a bunch of newer rental cars (including a 2019 Camaro SS), all I can say is that more than four is a waste in normal driving.

 

You can also consider a Gear Vendors OD unit. A fellow I work with installed one in his 427/TH 400 '69 Camaro and he's pretty happy with it. Have yet to see one installed in a GM A-body so not too sure about any tunnel clearance issues.

 

TCI makes a 6speed automatic that can be order with the BOP bellhousing. They show a starting price of over $5700. You'd have to call them about fitment

 

That's just a 4L80E where they gear split with the overdrive planetary. At least they've finally changed the ratios in the main planetaries, so first gear is now 2.97 instead of 2.48. The thing that scares me about this trans is that the 4L80E overdrive stage is the weakest part of that trans. In stock form it only has two clutch plates. I'm sure they beef it up for this application, but it's STILL a long way from the beefiness of the forward and direct clutch packs.

One does have to be skeptical of the hype.

Yeah, a trans that was first introduced in the 1991 model year is the LATEST development in drivetrain technology...

EDIT: the version that comes with a BOP bellhousing is a mere EIGHT THOUSAND DOLLARS!