I have a 2002 sunfire that had the 2.2 and 4t40. The mileage was variable and I was not happy with the amount of torque. I am working on installing a 3800 series 2 with a 4t60 with a 2.84 final drive. I can take the final down to 2.56 with a chain and sprocket combo. I am planning on a solid 40 mpg with the 2.84 final in there. The sunfire is 800+ lbs lighter than the donor car
The engine is in tip top shape, 200 lbs of dry compression and PLENTY of power. I should be able to climb mountains in 4th gear
Not sure if I will get it done this year or not, but it is in the shop and is half done.