My recently finished 5.3/4L60/NP205 into my 1972 Jimmy is running great. I had a few issues and now that they are cleaned up its like a whole different truck. Starts every time hot, cold, 50 times in a row! I have 31 inch tires and 4.10 gears and before with the 350/350 it screamed on the highway. I had the Jimmy doing 100 like nothing on the highway and there was plenty more. It actually runs so good I "might" need to rebuild the rear end sooner than I thought.
Just do it!!