I would keep it and build a fresh V6 for it. The truck does not owe you anything and whatever you get to replace it will have its own host of gremlins to be sorted.

I have thought several times that I should be selling my '87 and get a newer truck. I have seen a lot of appealing Dodges on CL and they would be perfect for towing a car trailer with the Ramcharger. But I don't need it yet and I also don't have payments either. The '87 runs very well, gas is cheap now, I have a new canopy on it and my dogs are comfortable and secure in it.

BTW 166K is not a lot of miles for a truck.