From what I've heard/read, it seems like the most likely cause for not being able to get out of first gear is a bad governor gear. Would that also cause me to not be able to manually shift from 1 to 2? I havent looked at my tranny lately to verify this, but will fluid be spewing from the cap when I remove it to inspect the gear? Thanks!

 

My experience has been that this has "something" to do with the governor. Stripped gear, stuck valve in the governor, governor screen is partially or fully plugged.

I suggest you do the easy stuff first. Remove and clean/inspect the governor.

 

I found an AC Delco part number online, listed as "Governor": 24202118. Is this just the gear, or the entire assembly?

 

I believe that is the part# for a remanufactured governor assy. What I have done is to go to the junk yard and remove several (many) TH700R4 governors. If I find a malfunctioning governor in one of my cars, then the chances are that I will have a good used one to replace it with.