Only way to tell for sure is to put all 4 wheels up on jackstands and put the truck in 4wd and see if the wheels spin. Or you could find a mudhole and see if the fronts pull.

Its pretty common for the hubs to be assembled wrong or for the spring to break. I have links to rebuild how-to's on my site

http://staff.4x4wire.com/adamf/88/hubrebuild.htm

88 4R, 350 V8, R150 5 speed Sold <...uot; />
97 4R, stock, daily driver
98 Sienna, kid and dog hauler, wife's ride