I'd like some input on my drivetrain troubles.

I pulled a small trailer through the mountains with my 1990 F-250 4x4 (351,zf5,1356). Felt some power loss (didn't feel engine related) towards the end and pulled over to let everything cool down. Ran fine, felt loss again, repeated. Got to my new home in hilly San Diego and really flogged my already tired drivetrain backing the trailer into a steep drive. Spat some fluid (maybe a teaspoon) from the rear diff onto the driveway and heard something external go "ping". I can now hear an intermittent clanging when launching, and granny-ing down hills and around tight corners. Sounds like a loose metal rod bouncing off something. Now, when I drive, first and second are strong, but third feels a little weak and fourth is weaker still. Also, fourth isn't as quiet as it used to be. At first, I didn't think it was the tranny, because it's still strong in the low gears and will still go through them all (dunno about fifth, haven't been on the highway), but maybe I just fried third and fourth in those mountains.

Anyone ever experience this? Thoughts?

Thanks in advance.

 

Maybe drain the fluid from your transmission and see how much metal is in it?

 

Where did the oil come out of the diff? I would pull the cover and make sure everything looks fine in there.