How much boost you getting before and after the HX35? What did you set the wastegate to? Ive got a 96 12 valve and contemplating on replacing the H1C with an HX35W
I don't have a good reference before swapping. After the swap, I get up to 32psi in 3rd and 35psi in 4th. That's with the waste gate locked shut. I hear that peak boost is not much different between the H1C and HX35W, but the HX35W spools up much easier. If you're looking for more power/boost, I'd check out a Borg Warner S300 or Holset HX40.
The HX35W is pretty close to the original turbo and didn't seem to bother MPG much. Starting with the flatbed dually, I only saw about ~18mpg, usually around 75mph on the freeway and some city driving. With the timing bump and similar driving, the best I've seen is 20mpg. Not a huge difference but enough to notice.