correct. if you look at the marks on your speedometer, you will notice the III mark around 75, that is the MAX rpm for 3rd gear. it should be shifting out of third into 4th at this point, unless your foot is on the floor... making the downshift switch preventing shifting out of 3rd. you could also have a bad kick down switch... a bad tranny, a bad shift linkage bushing, etc... fiddle with the shifter while you are around 65mph pop it into N and gently back into D and see what happens.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!