Never had a car with a 4T40 but did have two with the 4T60. My '99 Grand Am had a 4 cylinder but was still given the larger, stronger 4T60. Olds did the same with the 5th gen Cutlass, though mine had the V6. The 4T60 was only used on Chevy cars when they had a 6 cylinder.
Hmm, so Olds eventually stooped that low. They only used the 4T60E on the 5th gen Cutlass, regardless of the motor. Also, my '99 Grand Am had the 4T60E in spite of being a 4 banger. That car is still running but I don't own it anymore. I rebuilt the motor in the kitchen of my apartment after it spun a rod in 2010. Ground it for an 0.010" over bearing by hand. Amazing what you can do with a lot of patience and little money. It isn't like it was in the old days where you could go to the local shop and give the guy 5 bucks to let you use the lathe. Liability and such. The 4T60 will pretty much last forever if you treat it right.
Just make sure you keep the fluid clean along with replacing the filter everytime you decide to change the fluid, also recommend synthetic transmission fluid (dexron 6) to avoid any sort of overheating. Mine shifts way smoother with dexron 6. Edit: Also if the fluid is dirty, try not to change it since it could slip with new fluid.
