I was noticing yesterday and today that my truck seems to be charging higher on cold days more than warm days.On colder days it charges high enough to kick on the "gen" light is there a sensor somewhere that needs changed out to stop this problem?On warm days it charges normal.BTW the alt has just been gone totally gone through and all parts have been replaced

 

It is normal. The charging efficiency varies with temperature to track the needs of the chemical process in a lead acid battery.

 

...and the grid heater...
my volt meter used to go back and forth on really cold says as the grid heater kicked on and off. sounds normal.

 

I don't think that the Gen light coming on is normal. Yes, mine gauge swings just like everyone else's does but never got a Gen light from it. The sensor is under one of the battery's in the tray, forget which one.

Floyd

 

There is a temperature sensor under one of the batteries.
It's switched sides a couple of times according to model years so I can't tell you which side.
It looks like a spring loaded button in the center of the battery tray.
I've never run into a sensor failing or even becoming unplugged.
Problem I do see quite often though is when folks use a shorter than stock battery and put a spacer under the battery so they can tighten the hold downs enough.
The sensor has to be in contact with the battery or it won't charge consistently on hot or cold days.
A piece of wood or the spacers that come with some batteries don't allow contact.

 

After you start it on a cold day, disconnect the small wires on the two grid heater relays and see if the problem goes away. If it goes away the intake temp sensor may be bad. Worst case the PCM, but I doubt it. If it doesn't go away disconnect the wires from the battery to the relays, one or both may be sticking. The only time I have had the GEN light come on is when I forget to turn my grid heater relays off (mine are on a toggle).

on edit; never mind. I reread your post. The grid heaters drag the charge needle down, so that isn't your problem.