The full time 4WD models used a NP203 transfercase. I wasn't as strong as the other part time transfercase of the same era (NP205). NP203's are notorious for chain slippage as they wear, but aren't a bad transfercase really. They also had shifting issues, as the shifters were finicky and overly complicated. Part time kits were sold for NP203's, to convert them from full time. My truck used to be full time 4WD, but I converted it. I can lead to extra wear and tear on the front axle since it never gets a break. Front driveshaft is also always spinning, which can be bad in a lifted truck on the freeway (vibration is eminent). All the extra parts moving suck down more power and gas mileage too. I could feel the extra power when I converted my truck to a NP205, it was noticeable. I like the NP205 personally, no chain, rock solid gear construction, simple and reliable shifting linkage.