i have a 1980 k10 which was partially restored, anyways, when i drive in 2h or 2l everything runs fine, but 4h and 4l the front drive shaft spins but doesnt seem to give any power to the front tires, so what could be wrong? front axle u-joints? manual lock out hubs? or what? please help!

 

i would start by checking the hubs, lock them in and try to back up a steep hill, and have somebody stand outside and watch to see if your front tires spin at all. there is a primary side where most the power goes so one wheel should turn faster than the other side.. but if they definately arent getting any power the manual locking hubs are probably the culprit