Your transfercase switch is located on the top of the transfercase, like 6 inches infront of VSS. If you are on the drivers side of the truck you can gain pretty good access to it, ESPECIALLY if you have a body lift, I dunno if you do or not.
The T-case switch has a plug going in to it, so unplug it first and take it out with a wrench (not sure on size, prolly 20-21mm).
I paid like $23 for mine, but I have a discount at car quest through work.
What is your 4x4 doing at all?
Check your front diff actuator, I'm not sure, but I THINK 98 is the first year of the electric actuator, making yours a thermal actuator if I am correct, which takes a while to get hot and engage front diff, if you have that thermal one, take it out now and get yourself the electric actuator and the appropriate wiring harness (comes separate and is 100% necessary). The electric actuator shifts into 4x4 instantly (if everything else is working correctly). The brown wire on that new wiring harness splices in to the t-case switch brown wire.
Another thing to check (if you have the np243 electric t-case) is the encoder motor, sometimes those fail causing t-case to not engage/disengage in to 4x4, but often its just the sensor in the motor itself, which is almost as much as the whole motor itself, so that's 1 option you may have to consider.
Transfercase control module should be the last thing you check if all else fails, and those are expensive, but I have heard of connectors getting corroded causing problems.
Before I forgot, if you have np243 t-case, the buttons can get silly too causing engaging/disengaging problems, I think my cost for those were $48.00 at the GM dealership across from the Honda one I work at (same owner), and that also was with my employee discount. So they aren't real expensive.