Is there way way to keep the truck in fourth gear like the new models?

I had the same question a few years back with my 02. I spoke with my service manager and he provided me with all the info I needed. There is a 5th gear inhibit switch under bulletin number 02-07-30-051A dated Feb 14, 2003. If your dealer can't find that bulletin, PM me and I can either fax or mail you a copy (I'm heading to the lake today for the next week so I'll be out of the loop for a while). The cost at that time was about $500 installed by the dealer.

Dennis

http://www.kennedydiesel.com/docs/Allison%20OD%20lockout%20final.htm

Thanks guys that is what I needed to know.