So are there different boxes? I have the pump with the bypass tube instead of an evo so what gear box do I need?
Yes, there are different gear boxes. Either would work in your case. Visually, the main difference is the exposed snap ring at the input (stub) shaft on the 96 and under.
1997+ (EVO)
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Here is a 96, note the exposed snap ring...
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I run a 96 box (from Bluetop) on a 98 Tahoe with functioning EVO. It’s a noticeably tighter feel.
I had a “rebuilt” Delco that did exactly what yours is doing as far as return to center goes. Test drove it a half mile, turned around and yanked it back out. They either didn’t adjust the preloads at all or did adjust it and didn’t know what they were doing. It didn’t really matter.
Redhead and Bluetop are two manufacturers that have much better repair records. Bluetop rebuilds their boxes in the U.S. and I think Redhead does as well. There are a handful of others.