OK..I hope one of you has an idea what may be up with my Explorer now. I
took it to a radiator/aircond. shop to pull the rad and check it out, plus
service the AC because it seemed to be losing it's cooling power. My water
pump had some play in it, and was making weird noises, so I got them to Re
and Re that as well.

Here is where it gets stupid. The kid doing the re and re broke off one of
the bolts into the block, so to properly fix it, I was told they had to
remove the timing cover. I picked up my truck today and all is well.
Everything seems to be in order and looks normal. I pay the bill and drive
away but I only get about 3 blocks when I need step on the gas
hard......VERY strong vibration from the engine. It went away when I took my
foot off the gas.. I took it back and had the owner of the shop drive it. He
noticed it right away as well. We went back to the shop and put in under
load in front of his shop (brake and gas at the same time). It seemed fine.
I looked all around for loose plug wires and anything obvious, but nothing.

Now, after driving it for an hour, I have noticed a couple things:

It seems to be engine RPM related as soon as the engine climbs over 3000 RPM
it starts to vibrate badly. The fan clutch seems fine, as do the pulleys on
the crankshaft and all idlers.

Now, they had to remove the harmonic balancer to remove the timing cover. Is
there anyway they could have forgotten to reinstall any part of the
balancer.
I am very used to older chevrolets, but never had the pleasure of working on
a small block Ford.

I thought they may have jacked it up and bent the front driveshaft with the
jack , but it is not speed related ...it is RPM related.

any ideas for me to follow up on guys?   (and girls)
Kindly respond to this group.
Ken