C6 2nd to 3rd late shift

[NB_F100short]

Hello, guys, I've finally purchased a 72 f100 Shortbed. I'm new to posting here but have read so many helpful things. One thing that's wrong with my truck is that it shifts into 3rd gear very late. You either have to have the throttle down almost to the floor or let off all the way and when you give it gas again it will shift. When it does shift into 3rd it seems fine. 1st to second seems to always shift at the right times. I have done some reading on vacuum line problems, but don't know where to start. Thanks in advance for the help.

[tac]

Sounds like modulator valve is bad or or the vacuum line going to it is loose. There is a metal line with vacuum hose on both ends that goes from the bottom of the carb/intake to the back of the modulator valve on the back of the transmission. Check the line first and then pull the rubber hose off the modulator and see if there is any transmission fluid in the line. Fluid means the modulator valve is bad.

[NB_F100short]

Sounds good, thanks for your help!

[colnago]

My 352 is worn, has two burnt intake valves, and as a result, has low vacuum. In cold temps, it takes forever to shift. At first, I thought it was my tranny, but it ended up being my engine. Just my two cents.

Joseph