88 930 difficulty at speed changing gears
 

At highway speed I could not get into 3rd, 2nd, or 1st gears, but with effort could slip back into fourth. This happened suddenly while on long trip. Decided to pull off freeway into gas station, after stopping I could shift into first, second etc. Got back onto highway and up to speed and again could not change gears. Repeat above.

Any ideas on the cause.

Oil level?

changed it lately?

How do your engine/trans mounts look? Are they snug? --could be driveline flex?
Where does the clutch engage in the pedal travel? --- maybe as simple of dialing in more clutch?
Bill K

rubber hub clutch disc chunks blocking pressure plate release?