1984 300D

From a stop slips through first gear.

When driving 5mph up a steep hill, will downshift into first and climb the hill fine.

When parked with parking break engaged, won't slip.

I am ordering the vacuum switchover valves, as the levers are worn off.

Plenty of vacuum at the check valve on the booster line.

15" drops to almost zero when accelerating, at the valve on top of the injection pump.

The line to the modulator holds vacuum.

Doors lock fast, car shuts off, brakes work great.

If I power brake it a little before starting out, first gear engages fine until next stop.

Red trans fluid, no burnt smell.

Can defective switchover valves cause this problem?

Any other vacuum I should test?

Also, this wasn't a problem that got worse over time. I parked it on Monday and it had driven fine, and on tuesday BAM just started slipping. I have 500 miles on the car since and things have gotten no worse.

Also, when a shop was replacing the master cylinder, they broke the orifice off the check valve on the booster line, and rigged it with an old piece of vacuum line (I since have replaced the entire vacuum booster line). Could that hack fix have affected my transmission?