FMX Shifting at 6000+

I know this is a c4 forum but hey they all do basically the same thing. My deal is, ive got a 69 mustang 351w with a 3speed fmx. Going from 1st to 2nd is no problem at wide open throttle. It shifts around 5000 and chirps the tires but if i stay in it and wait for it to shift into 3rd, it winds out to like 6000+ and wont shift till i let up and the rpms come back down. This happens whether i put it in "D" or manually shift it. I did just put on a different intake and a 4.30 gear (previously had the stock 3.00 gear). I didnt have this problem before. I know the vacum will change with the intake but i tweeked the vacum modulator a bit. I am fairly familiar with that part of it. And yes i am getting vacum to it. I know theres less load on the transmission because of the gear so would that have anything to do with the governor? Any suggestions on what i should do?

Governor problems.
Very common when you swap out rear gears.

In addition, shift kits are still available for the FMX.

why would swapping rear gears have anything to do with the governor? It still opens a valve at a predetermined shaft speed. That speed will still be the same, but the WHEEL speed will be slower due to a little bit more gear ratio.

I'd like to learn more on this subject. Not really all that familiar with the FMX.

it definately doesnt need a shift kit. chirps em pretty hard and sometimes even into 3rd. About the governor...the whole tail shaft has to be removed to replace that right?

Sounds like the valve body is sticking, Does this car sit alot or is it daily driven? You are not using B&M Trick shift in it are you?

A friend had the same thing years ago. He got advice to back off the kickdown a little and sorted for him.

The car is driven pretty regularly. was daily driver until about 2 or 3 weeks ago. no b&m trick stuff. all stock. i dont have a kickdown rod because the high rise intake messes up the geometry of it. I guess ive narrowed it down to more than likely the governor and maybe the valve body. thanx

With the lower gears there is less load on the transmission and higher rpm - It messes with the relationship between line pressure and modulator pressure.
The FMX is known to have sticky governors too - try removing the spools and polishing - lube with Vaseline and reinstall.

Sounds like a plan Paul. Thanks