I just bought a 2001 Yukon XL with the6.0 and awd. It has about 115000 miles..Can you with what maintenance and services need to be done to this truck

Yes I would also flush the system and change the filter

Without hearing it, I can only guess. Collapsed lifter or loose connecting rod bearing.

High miles? Maintenance not done on schedule? That would do it.

Dunno! How many miles do you have on it? Have you change the fluid before? At what interval.

The coolant and the belt.

A mechanic would check for voltage at the starter, the neutral safety switch, and the key switch. Then check the battery cables and ground connections.

coolant doesnt evaporate out of the engine. it has to be going somewhere find a shop that can add some uv dye into your radiator and check for leaks

General Motors does not have a service interval for fuel injectors, though they make a injection cleaner if there is a drivability issue. Other companies suggest a injection cleaning interval of 48000 miles. I would suggest an in tank additive from a reputable company every couple of years.

I NEED THE CODE FROM THE TRANSMISSION CONTROL MODULE. THIS IS NOT FOR SERVICE.

My 2000 Yukon XL with 5300 engine had same problem at 115,800 miles in Aug 2006(I bought the vehicle new January 2000)...My GMC dealer did diagnostic and replaced a faulty 4WD Transfer Case Shift Control. (reading from the service invoice) It was GM part number 15709327. Cost for the repair was $41.48 + labor $74.13, total was $115.71...it now has 165,000 on it and so far no problem and the 4WD works when I need it.

coolant flush and fill.. differential oil changed out ( assuming you have done trans service already also ) .. driveline (u-joints) and steering linkage lubed , fuel filter(s)..and all belts /hoses inspected ... have fun :)