mhill73

Hello all. I have an issue with my 99 sport 4x4 that has even the mechanic stumped. I recently had to have the rear differential replaced due to imminent lock up. before the swap, my rpms at 70mph were around 2200 to 2400 rpms. After the swap, they are now 2700 to 3000 rpms. the mechanic assured me that the tags for both diffs matched up. took the mechanic on a ride and see confirmed that the trans is functioning normally but I am in the early stages of needing u-joint replacement. the truck has 239,000 miles but I've kept it well maintained. the trans was rebuilt last year @ 230,000 for a bad band between 2nd and 3rd. any input as to why the rpm change will be greatly appreciated. Thanks in advance.