if the owner will allow you take the turbo inlet tube off and check the fins on the impeller for nicks - this is caused by poor filtration
check the intake box for cracked or broken clips that would prevent the filter from being sealed properly
check the heat foil on the firewall for black soot around the back of the motor, that would indicate an up pipe leak which will increase egt's and decrease milage and power.
smell the trans fluid if it's an auto - burnt smell could indicate abuse or lack of maintenance
make sure the heater/ac controls will switch to all the different vent/defog positions, if this doesn't happen the truck most likely has a vacuum leak or a problem with the vacuum pump or circuit, this vacuum pump also controls the auto locking front hubs.
check 4wd and transfer case motor works (must be in P or N to get into 4wd Low)
glow plugs can be a service item on these trucks, while it can be hard to tell in the summer, if the owner has the truck plugged in you'll know for sure it needs new glow plugs, it would be best for you if the truck hasn't been started in a few days and be there for the first startup to check for smoke colors if there is any and how long it takes to start, also both batteries should be the same brand and same date, these trucks have dual batteries and they need to be replaced in pairs.
drive the truck, make sure it's well warmed up, listen, or feel for unusual knocks or misses, check the dash for service engine soon light, watch the shifter stalk for flashing OD light (trans problems) when the truck is warmed take it for a spin, normal operating temp for my truck is about a quarter inch above the bottom of the normal range on the gauge. make sure you pay attention to how the truck shifts watch for slow sluggish shifts could be a sign the trans is on it's way out.
if you let it idle by itself you may hear the exhaust note change to a tubine like sound, that is normal, it is the exhaust back pressure valve closing to help the truck warm up faster, it should open the valve and go back to normal as soon as you touch the throttle.
also if you can get a jack under the front diff and slightly raise the tire each side at a time and put a pry bar between the tire and the ground see if there is any play in the ball joints up and down without suspension travel, any play is bad and they are a pain to replace, could be $1000+ job at a shop
also while your driving make sure you notice how tight the steering box is, (in BC Canada only a 1/4" of steering wheel play is acceptable by law) side to side of the steering wheel without steering movement is not good... sometimes this can be adjusted out but a new steering box should be on the to buy list...
Last edited by Phiber Optik; 08-20-2010 at 04:58 PM.