I understand your frustration, but these are 25+ year old trucks (and electrics). 128k is not uncommon for these engines and they easily run twice that if properly maintained. It sounds like you have a minor issue with both your engine and your mechanic's competence. I have a rebuilt 3.9 in my truck and it is as reliable as an anvil. I pulled the old engine at 140k to find the only real problem was a badly worn timing set (I do no like nylon timing gears). If the compression is good, and not burning oil, I would fix whatever minor issue you are having. If you are hard over on a R2.8, do as @Red90
suggested and call Uncle Doug.