The 53 block is not that common so dont loose your mind about that. We're just pointing anything that might go out on these trucks. Its 12yrs old. You dont know who owned it before or how they drove it. It could of been babied or abused. You dont know. The auto trannys in theses trucks are not very strong. If you have high HP dreams either look at a full replacement tranny thats built or look at a manual truck. The front ends wear out on any truck. 150K miles probably getting close to needing balljoints and a few other things but thats normal maintenance on any truck of this age and mileage. DO NOT just put it in 4wd and gas it!! First put it in 4wd H and turn the wheel to the left and right as far as it will go, start turning in a circle, and if you feel a jerk in the steering wheel you know the front end is engaging. Someone might have a better way that just how I check. You will know when you feel it start to jerk the wheel. To test 4wd Low all you can really do is put it in low and make sure the transfer case is engaging. If the dealership will let you take it to their service area and jack up the front. Most will if they are trying to sell the truck. Wiggle each front wheel. If there is play it is time for ball joints. Could probably negotiate that into the purchase. First thing this truck would need is a lift pump. The lift pump on these sucks and can cauise the injection pump to go out. These trucks are totally worth it. I have had my 24v since 2004. 8 years and 170K miles later, I love it more than my 6.7, and there isnt a price that could by it.