Found my problem - I had removed a plug that is located behind the glove box and goes into the engine bay through the fire wall, well, that is where the instrument panel is grounded. The only reason I removed it was to get the stock wiring harness out of the way for my install. Both water and oil gauges are functional. The tach also works but is about 600 rpm shy of reality. How do I fix that? Can I do it with my HP Tuners?

I had a thought with my fuel gauge issue, and yes I know it may be extreme. I'm thinking of getting a newer fuel tank from a Suburban to replace my 98's. That way I'll be running the newer fuel tank and fuel pump assembly and should have no issues with the LS ECM reading the fuel sender. The only issue that I see could be that the stock 98 gauge would still not read the info coming from the LS ECM - does anyone have any experience with this?

I did drive it up the road the other day - this 6.0 has a lot more power than the old, tired 5.7! Thanks Lextech for your help with the wiring - retrofitting the stock 5.7 harness to the LS engine is the way to go......For me anyways.