Hi all.
I just manage to resolve my problem with my transmission which was slipping due to malfunction of the venturi solenoid.
The problem I am faced with now is the change from 3rd to 4th. It happens only at 4,000 rpm and then cannot stay in 4th in low rpm unless I further increase speed.
Could it be low pressure in the transmission (shouldn't I have the same problem with 2nd to 3rd in this case?) Or what else could cause the problem?
Lurtch proposed to check the vacuum taps in the intake plenum, I could not see any issue there.