I have a stock 454 tbi out of a 2500 pickup with 150k. I have the computer also.

I would like to get at least 20mpg on the highway.

What would be the best trans 700r4,4l60,4l80? Going in 88 camaro.
And what rear end?

Will never see the strip, just a cruiser.

20 mpg is gonna be a challenge to hit; the vehicles these were coming in were averaging in the teens. according to the info i found, the final gear on the 4l80e is 0.75, where as the 4l60e and 700r4 are both 0.70 (advantage here). you're gonna need a wimp of a rear to bring those numbers higher.

150k on that motor's a bit on the high side, if you want to get any life out of it, you're going to need to get it rebuilt. if you're looking for that kind of mpg AND a boost of power over what these cars came with, you may want to look into doing a 5.3 swap

Depends on the exact year of the engine. My 91 454SS has a TBI. Pushing a 4600 pound truck with 4.10 gears and 28" tall tires, it only gets 10-12 mpg in the city and it has the 4L80E tranny. The lighter car will help that out and keeping the gear ratio in the mid 3's will help even more.

The TBI 454's were not big on performance. Good torque but HP only peaks at around 260. The limiting factor is how much fuel can be pushed through 2 injectors. The NHRA Stock Eliminator rating is only 310 HP.

My 91 only has 170,000 km on it. Mileage looks high but for the age, it's still low.

If you can afford it, the 4L80E swap would be the best. You need something that can handle the torque. If the diff gears are not real deep, a basic TH400 will also work. As for the diff, it's like any other engine that makes lots of torque, you can try making the 10 bolt live but will probably have to upgrade to a 12 bolt, 9" or Dana 60. My 454SS has a 14 bolt 9-1/2" diff from the factory. Basically it's a 3/4 ton diff with 5 bolt axles but it's also a truck designed to carry weight. It would be overkill in something like your car.

What about a 3.73? I drove the truck before, the motor is very strong. Its just sitting on a crate in my shop now. I might just sell or trade for 350 vortec.

I also have a good 400 trans.

If its just a cruiser why put a truck 454, a 350 vortec bolts in and will handle better than that 700lb. lump. Use the 700R4 with some high rear gears & keep the engine rpm down to 2000 RPM at 70 MPH or so. Thats just my opinion, just like A** H***s everybody's got one!

One more thing about the 454, if that truck was used hard like camp trailer towing Iv'e seen allot of these cranks cracked at rebuild time, not broke but still needing replacement. Chevy got a little cheap with the cranks compared to (and i hate to say it) a 460 Ford, YES I said the F word-sorry.

Well the motor was already rebuilt before, the old man kept the maintenance up on the truck. Never used hard as slow as he drives, mostly highway miles. I really like the budget tbi vortec build

tbi 454 is a very reliable engine. lots of torque but not a huge performance engine in its stock form as some mentioned. i believe with the a lower set of gears you could pull off mid to high teens but i think 20 is pushing it but possible.

Highway miles? if I can get close to 18 ill be satisfied. I will be purchasing a 3.73 posi rear