66 olds not shifting out of 2nd gear

Just took my 66 olds dynamic 88 out of storage. Runs good but not shifting out of 2nd gear. Fluid is fresh and so is filter from a pan gasket leak fix last year. Could it be the modulator? Haven't had much time to check yet...how can I tell if indeed it is the modulator?

If the trans is modulator equipped, check for vacuum to it. If good, replace it , cheap enough.

replaced the modulator, have vacuum. was down a quart of fluid. filled it and took it for a ride. still not shifting. its actually not shifting out of 1st from what I can tell. car had a trans pan leak that was fixed before it was put in storage. as far as I remember it shifted fine 2 years ago. it goes into drive and reverse very solid without hesitation or slipping, fluid doesnt smell and still looks fresh. I live on a dead end and maybe...just maybe the street isn't long enough for it to shift? has no exhaust at the moment so its loud regardless. going to re check the fluid and try it on a longer stretch tomorrow. praying the trans is ok. hoping to get this car safe and reliable for some cruising this summer

I should add...its got a 425 with a 3 speed auto (turbo 400?)

If it is a THM 400,,, disconnect wire on the side,,,if now works,,passing gear switch is stuck (on),,,,,if not ... suspect governor is damaged or stuck

Turned out to be a clogged steel vacuum line to the modulator. Had vacuum when tested at first but then nothing. Jimmy rigged another hose and she shifted through all gears like a champ. What a relief. Off to the parts store to try and replicate the original steel line the best I can. Thanks for the help!

Looking online for new modulator line. Do I have to get a stock line or can I make my own out of steel tubing of the same diameter with rubber hose ends? I notice they sell pre bent replacements but of course I cant find one for a 66 dynamic 88

You can make one up, same diameter as you said.