I know that case pretty well as i have had 3 trucks with them. both of mine felt that way too but were working just fine. You are probably feeling the shifter detent ball coming up as you try to push it beyond it's 2wd position. If you have lockouts unlock them, put the t-case in 2wd & crawl underneath & your front output driveshaft should spin freely. should not turn in 4wd. if it turns but goes "click click click" in the transfer case then something is needing attention in your t-case.
Also, in my experience this rockwell burns out the bearings on the uppermost shaft easily if it is ran low on oil as the splash has quite a way to go to get to them. I filled my oil with the truck leaning on a slope to raise the fill plug a little higher to overfill it a little & that seemed to help.
Don't be alarmed by some gear whine as these did that when they were new. -jeff
