That is weird, definately something that should be checked out, my 89 v6 SWB is fairly peppy and with a couple inches lift and 31" mudders I don't really feel comfortable taking it past 75 ish but it has no problem getting there and I'm positive I could get it up to 100+ on the flats. Might be time for a good old tune up.. you could check fuel filter, plugs, cap & rotor, wires, maybe run some seafoam through the fuel. If you find something out, let us know.

1989 Mitsubishi Montero SWB V6. Torsion bar crank, Gen II springs, 31X10.5" BF Goodrich M/T's
2005 Mitsubishi Montero Limited 3.8 V6
2011 Subaru Impreza Outback Sport