I would get it to the shop as soon as possible. I purchased it new, and it now has 175,000 miles on it. I have changed the oil and filter every 5,000 miles, and replace the antifreeze annually. I've been told that this engine is subject to blown head gaskets, but I have not had any problems. The engine uses no oil, and runs like a top.
Oil pressure is excellent and compression on all cylinders is correct.
I have never owned a vehicle like this that never had had a single problem. It's been a great pickup. Although a lot of engines don't make it to 175,000 miles, I think your mechanic is wrong in suggesting that yours will soon need an overhaul because of its high mileage. The good oil pressure and consumption, coupled with cylinder compression that is even and close to factory specifications, would suggest this engine has a lot of life left in it. However, I think your mechanic is correct in suggesting that you let sleeping gaskets lie.