99 ford ranger - transmission problems

99 Ford Ranger, 6cyl 3.0 Flexfuel model, 140,000 miles, but I keep up with oil changes etc. Running normally until today - after being running for about one hour, I made a U-turn, and shifting suddenly became very difficult. I was able to shift gears only with effort, and I could hear “grinding” akin to when one tries to put the car in gear without depressing the clutch.

I strongly suspected something was wrong with my transmission/clutch. That I had just had an unnamed large chain mechanic shop change the Manual Transmission fluid only added to my suspicions. I brought my vehicle back to their shop to be inspected - the indicated that the fluid levels were correct, but offered to add some MegaLube goop for good measure. I noticed that the transmission fluid coming from my truck appeared dark, even though the fluid had been changed only days prior.

My vehicle improved marginally after leaving the shop, but still occaisionally has strong difficulty shifting at times (especially into 1-3rd gears) and the grinding continued - sometimes even after putting the car in gear.

I took it to my regular mechanic (don’t ask me why I didn’t take it to him for the oil change - I was too lazy to make the drive to see him, and I was in a hurry to just get my oil changed), and he believes that the chain store may have added the wrong kind of transmission fluid. My receipt lists Penzoil Dexron ATF, though my vehicle is a manual and calls for Mercon. I remember from working at an auto supply store that Mercon and Dexron are generally sold as a dual-use combination fluid. I’m confused about any number of things: doesn’t ATF stand for automatic transmission fluid? Could putting a dexron/mercon V dual use fluid into my vehicle cause transmission damage?

Thanks ahead of time for your reply. Heres hoping for the best.

MG from Portland

Still looking for a hand!

The thing that I see that stands out is, this didn’t start occuring until you made that U-turn. So I’m thinking that something with the engine/tranny mounts, or if the tranny mounting hardware to the engine is loose, and when you made that U-turn, something shifted in the drivetrain. That’s what I would look for.