First look at the drivers door sticker and see what gearing it has, AXLE code: Ford 7.5 & 8.8 Inch Axle Tag & Door Codes
And on the same label will be stock tire size it came with.
"normal" gearing(axle ratio) would be 3.73
4.10 has better pickup/acceleration/towing, but lower MPG at speed
3.45 has better MPG at speed but lower acceleration and towing power.
Original buyer may have wanted best MPG for commuting so ordered truck with 3.45 or even 3.27 gears
Larger diameter tires lowers axle gearing, and the lower the gearing the less acceleration power you will have.
If someone installed "taller" tires then that could account for some loss of low end power.
Restricted exhaust, usually it shows up at higher RPMs, like the old "potato up the tailpipe" but more subtle.
Vacuum gauge can test for that, vacuum gauge can also tell you about compression, 3.0l ran 9.3:1 so should see about 170psi on compression test.
You are above 2,000ft elevation which will reduce intake vacuum and compression a bit but not too much, and because of this higher elevation all engines can seem sluggish, which explains why every other car is a turbo when you drive in citys above 2,000ft.
Restricted air intake, check air cleaner and the CAI(cold air intake) tube that runs to rad support.
The 1996 and '97 had the lowest torque rating for the years of the 3.0l 162ft/lb, 1998 had 172 and 1999 and up 190ft/lb