I have a 1991 GMC Jimmy with a NP241 C transfercase. Recently the transfercase has been acting up. There is no 4high at all and when I put it in 4low it grinds gears. The transfercase has been dropped for as long as I've owned the truck but the problem only started after I lifted it and made a run on some trails. I pulled the t-case and opened it up yesterday and found that all the gears and and the chain look to be fine. What is wrong with my truck? The linkage, the transmission, the transfercase?