I had a 79 with a 74 350 110,000 miles and a th350/203 in a halfton. Upgraded to a different truck with a 350/th400/203 in a 1 ton. Took the blown 350 out and put the same 110,000 mile 350 in and I dont notice a bit of difference. All I know is the th400 has 300,000 miles on it (5 motors over the years w/ out a rebuild on a construction truck) and it still works fine. Power output is the same and I noticed a little gas mileage suffering and thats probably due to the 1 ton axles vs 1/2 tonners. Once my th400 goes out im ready for my 700r4 doubler combo. I like overdrive and lower first gear personally.