EZ Dodge Cummins Questions

I had an 89 5 speed when they first came out, one of only 2 new vehicles I've ever bought. Mine was 2wd though. Mods I made were, removed the muffler and installed a straight pipe, it wasn't that loud especially inside the truck. Next I advanced the pump timing to 1.30mm and upped the rev limiter to 3100 rpms. I could get 26 MPG towing an open trailer with a car on it doing 95 MPH on the highway.