Tank your claculations are off. 1/4 wave is app 9.8 ft.
SpenceIFD what about raising the antenna on the jeep to a higher area. You should get good transmission and reception with the 102 whip however if it is low on the jeep and close to the body you could be limiting the performance. Something like a hood channel mount. I have mine off the windshield light bracket. the 2 ft Wilson does well there. I've seen guide vehicles on the hi way with a mast & antenna up to 20 ft. But that was just a raised antenna.
Also if you looked through the Firestick tech info I linked up there is a section on how far you could transmit and what limits the transmission. If you haven't already I suggest you take a look.
"Never look down on anyone unless your helping them up"- Jesse Jackson