I have a 1990 5.9 Cummins swapped in a 1990 F350, Getrag and 4.11 rear. which I've towed all kinds of stuff. Just lately I towed about a 14,000lb fifth wheel RV and it really made the old 12V work. Really felt underpowered. It is all stock and great condition as far as I know, just changed filters, etc. Not sure how many miles on the engine, maybe 200K. Does this sound about right? I've never driven another another 5.9 cummins to compare. I'm thinking about doing a compression check, just to do a double check. Time to start thinking about some mods maybe?