Horror Story: My 300SD is Falling Apart...

[regsatx]

I've had it only since September 30. It was love at first sight, silver with remarkably preserved grey leather for an '85 SD with 224k on the clock. She handled great and ran superbly, at first. I drove her home 120 miles from where I bought her and she ruled the road, gliding almost effortlessly at 75mph while giving a cloud-like ride. Within a week, the honeymoon was over.
I posted an inquiry on this forum about vibration recently. I adjusted the idle, bringing it up to about 850-900rpm from 750rpm. It was OK for a day or so. Now the vibration has returned and something more ominous has surfaced. The transmission slipped a couple of times this morning. Then, on a subsequent trip, it would'nt upshift in Drive. I had to drop it into 3rd to make my brief, low-speed trip. Could a transmission go out that quickly? Did my adjusting the idle screw on the injection pump have caused this?
Guess I'll have to take to a shop to find out. I appreciate any suggestions...

Disappointed with my diesel