Does the engine make any noise? when was the last time the fuel filter was changed? can you check fuel pressure and take a fuel sample?can you check compression for each cylinder?did the engine recently overheat?
I have seen an explorer before not run from fuel contaminated with water. I would make sure we have goof fuel pressure(30-40 psi) and the fuel sample does not show water or is not cloudy. These engines do have a complicated design with timing chains and valve timing, I could see why Ford dealer would say 200k check the timing. There are special tools to check, set and align the valve timing and in most cases with replacement or repairs the engine needs to come out. The cam sprockets do have any pin or lock so they can spin or slip(poor design)
good to check fuel sample in a clear glass/plastic container. If you let it sit it will separate. this is what high water content looks like, some samples can look very dark with other contaminates.
I just drained the tank, put new gasoline in it, just to discard, same problem,
the question about timing issues is if that were the case would I be able to maintain a constant acceleration between 800 and 3000 rpms?
im able to control it up and down in that range and the engine runs mooth, but it does not go over 3000rpms, when i leave it idleling, the engine runs good for a minute or so and then starts to choke and dies, it seems like the gases choke the engine.
what is the fuel pressure?
what were the compression readings? Do you have access to a scanner that shows live data?I would like to check fuel trims and what the 02 sensors and MAF sensor is doing. I would check to see if the valve timing is off. If you pop off the valve covers you would be able to see when the engine is set to TDC on #1 cylinder.
if you can check the coolant temp sensor. I remember older explorers having running issues with bad coolant temp sensors.