When im crusing at about 60mph if i let off the gas the RPM's on the tach wont go back down and i dont hear the engine go back down in speed it just stays where it is buut before it did go back down, could this be overdrive related?

 

Sounds more like the throttle return spring the way you describe it. What happens when you put it in neutral? If it's the same then it's not the trans.

 

An automatic won't go back to idle when you let off gas - the engine is still going to turn the speed of the car (of course accounting for rear gears, tranny gearing, etc.).

Neither will a manual, unless you depress the clutch and disengage the drivetrain.

 

I know it wont go back down to idle but it does go down in neutral but before this started after i let off the gas the RPM's would drop down aand now it wont do that

 

Auto or manual when you take your foot of the gas the car should slow down and the revs drop. When you're at cruising speed and you put the trans in neutral and your foot is off the gas does the engine go back down to normal idle? From your description it sounds like when you are cruising and you take your foot off the gas the car maintains the same speed. Is that the case? Do you have cruise control?

 

What gear are you in then, and what speed does the tach show?

 

Im in overdrie so my 4th gear if i shift down into drive the needle on the tach goes up, when im driving at about 60 it usually sits around 2500 rpm's. I do have cruise control but i usually have it turned off

 

So, if you are cruising at 60 and you take your foot off the gas...
1. The rpm drops and the car starts to slow down?
2. The rpm doesn't drop and the car does not start to slow down?

1. is normal.
2. means something is wrong with your throttle control somewhere. Sounds like the return spring is not closing the throttle. Check the cruise control linkage is not binding or stuck. Try removing it from the throttle arm and see what happens. This does not sound like anything to do with the transmission as such. Except as it's linked to the cruise control.

 

The rpms do not go down and the car slows down

 

After all that is said above...that makes no sense.
perhaps if the car is put in neutral it would do that but I can't see it in Drive @ 60. Surely the engine would have to dis-engage from the drivetrain for that to be possible.
Do you hear the car still rev while you slow down?
Could it possibly be a problem with your tach?

 

Apart from the tach do you hear the engine rpm drop? If you take your foot off the gas and the car slows down the rpm must drop. Does sound like a bad tach or something connected to it.