The 88-98 Chevy C/K trucks are notorious for taking quite a while to engage the 4 wheel drive. I drove one for about 3 years at work. I would use the 4 wheel drive in the snow. The truck was an 88 K1500 with a 350 V8. These trucks have an electric type actuator in the front axle. This element heats up and expands a gas in the front end, which in turn engages the front axle. This is what is taking your truck so long to engage into 4 wheel drive. Is your truck an automatic? The one I drove at work was, and i would do this to make it engage faster. I would come to a complete stop..shift the truck into neutral..pull the lever straight back into 4HI..wait a second or 2 then shift the truck into drive..then the 4/4 light would come on almost instantaneously. Waiting for the truck to go out of 4/4 would take about as long as waiting for it to go in. First i would come to a complete stop, then i would again..shift it into neutral (trans)..put transfer case back into 2HI...shift transmission in reverse..back up a few feet..then shift back into drive and the light would always go right out. If i didn't do this it would take forever to disengage. Hope this helps.
I have 2 trucks 88-99 with the system,and they take about 7-10 seconds to engage.GM changed them over last year to n electric actuation,the good news is that they retro-fit right into the older trucks,they are around 60 bucks at my dealer,if mine goes that is what Ill put in.It is vey easy to change them,about a 5 minute job.
I had a Jeep Cherokee(1990) that was hard to get into 4 wheel drive. The dealer told me that if the tires are worn bad, sometimes that keeps the system from engaging. Sounded strange to me , but after I got new tires on , it worked fine.
The 88-98 used a gas charged cly. with a heating element. The element heated the gas in the cyl. which expanded then moving the cyl. At your local dealer there is a new actuator to fix this minor inconvienence(which isn't so minor when you run into a big drift).The new actuator uses an electric servo which engages the front axle as soon as you pull the lever or push the button.It is also alot more reliable than the old style.Not IF but WHEN this one fails I strongly recomend that you replace it with the new style.It's more money but well worth it.