My transmission seems to be stuck in the lower gear. If I let the car get up to speed in neutral and put in drive then the upper gears seem to work. This is probably not a good idea but I did a lot of test driving and playing. I first noticed a problem the day before when I had to maintain a high RPM to go 50. I assume I was in 2 or 3rd gear. I was able to stop and play around with the transmission and was able to get it shifting again to get home at a reasonable speed and RPM. Now I cannot get it out of low gear without by passing the gears. I checked the fluid and it was low but I filled it and it still did not shift. I'm hoping it is the bowden cable or the vacuum supply or modulator. Any ideas where I should look.

Thanks