Took my 96 Yukon to the dealer for hesitation/"stuttering" at highway speeds when attempting to accelerate from 50-60mph while in overdrive gear (much less of a problem in third gear). Changed 8 injectors, 2 oxegen sensors, and dist. cap; all to no avail. Dealer told me it was likely "deeper" in the valve system. Rather than spend the money on that (engine had 188K) decided to replace engine with used. Guess what? No resolution to problem. Any advice?

You swapped the motor and you still have a problem? Was the old engine setting any SES light codes when the hesitation would occur? What I mean is could you diagnose the problem as an engine misfire?

Also, when you did the motor swap, did you use the old PCM and wiring harness?

First thing I would do is have a fit at the Service Manager or General Manager at the dealership.
Second, I would take it somewhere else & have them start from the basics. It could be a fuel or ignition problem.

At first, the SES light did not light. Eventually, it did, which prompted me to take it to the dealer. The wiring harness and the PCM were not changed with the motor swap. Incidentally, the mech who swapped out the engines (not the dealer) claimed that he did not believe that the fuel injectors,which I had told him were brand new form the dealer, had been changed (looked carboned-up and the intake manifold looked untouched). Any way to check numbers on the injectors and date them?

Mass air flow sensor..
I would have went there first before any of that other crap. You might be getting raked over the coals. I would take it for a second opinion

it sounds like a maf problem to me as well.