there's a small plastic cup in the shifter lever of the trans... these wear out and can make the shifter feel like rubber... check that, and the bolts while you're at it (you'll have to take them off anyways to replace the cup.)
also, have your trans flushed and replace the fluid with a good ATF (redline, or mobil, IMO)... NOT GEAR OIL!!!... bad or burned or worn out fluid can cause a "gooey" shifter feel, as well...
after all that and you're still not satisfied, get a new shifter (of all the ones i've driven, my preference is the JTSVP gen2) but there's plenty of used options out there...
:itsme::itsme::itsme:i also think you should throw a Cummins badge on the front fender
:itsme::itsme::itsme: