My 95 PSD gets about 17-18 driving 60-62 with 4.10's unloaded about 22-2300 rpm. If I go 55 it jumps to about 19 running 2000 RPM.

With the open trailer running 60-62 about 16.5-17. If I run 70 it might get 15 and at 75 about 13-14. Luckily I'm rarely in a hurry towing.

Only mods to the truck are a fresh air intake and 4" exhaust. I may get a 4 position chip to see if it will help and was thinking about pulling the 4.10's for 3.55's. My trailer doesn't tax the truck like some of you have. Only a couple of grades I've had to pull out of 5th going up a hill on the highway