hello
I recently bought a used Ranger 3.0 automatic with 102k miles from craigslist, it looks pretty good but has a pretty good "shimmy" when it shifts into high gear. on the test drive I assumed it needed good tires,which it did and after getting a set put on it smoothed the ride out quite a bit but still starts to shake pretty bad when it shifts into high gear. I replaced the plugs and wires and replaced the air and fuel filters. which is standard when I buy a clunker off craigslist.

If anyone has an idea what could be wrong, I'm all ears
thanx

 

Could be the axel, Had the same problem with my 96

 

If you shift into Neutral while going down hill at "shimmy" speed does the shimmy stay around or does it go away.
If it goes away then shimmy is from engine or trans
If it stays then shimmy is from drive shaft, axles or wheels/tires

 

its definitely from the engine, it goes away in neutral, also if i let off the gas for a sec and dont try and accelerate, or if I floor it and it downshifts it also goes away.
I also noticed it does it at idle in gear then when I take off it runs fairly smoothly, until it shifts to OD, could it be the EGR? IDK this is my first ranger and I love the truck, we still drive it around it would be nice to have it running properly

 

Could be OD drum is out of round, but wouldn't explain why it shakes at idle.

Not a Ranger issue, just general automotive issue, nothing sticks out as a 1999 Ranger 3.0l or a 4R44E trans issue.

EGR valve is not used when engine is cold, so if you still have shimmy when engine is cold then won't be EGR system.
After engine is warmed up you could remove the vacuum hose on the EGR valve, and then plug that hose with a bolt or screw.
Drive truck and see if shimmy is gone, CEL(check engine light) will come on after a bit, because EGR is unplugged, it will go back off after a bit when it is plugged back in.