Gmc 1500 Automatic Overdrive Converter Question

[keckjr]

I have a 1991 gmc sierra 1500 2wd 350 automatic overdrive. My question is whether the converter is supposed to be locked up when your running down flat road with hardly any load? My truck will unlock the converter when there is no load on the transmission. But if you start up a hill it will lock up until it gets to flat-ish ground, then it will unlock again. If your getting up to speed normally it shifts into 4th then locks up the converter shortly after depending on throttle. But as soon as the vehicle gets up to speed and the motor is no longer loaded youll hear it unlock and the rpms go up slightly, at that point you can give it a little more gas and it will lock back up. I do alot of driving in the ozark mountains and cant afford putting a new transmission in it instead of figuring it out before it tears something up. It just seems like if it was operating normally it would lock up the converter at all times (in 4th) except when you start pulling an incline that would require more power. Then I could see the need for it unlocking. Please any help would be appreciated and probably help to save me alot of cash.

[2COR517]

Probably should take it to a transmission shop for a test drive.

[keckjr]

I thought id add, it does have alot of mods including a hypertech chip. I could understand how that could change when the converter locks and unlocks. But im not really sure if it is even a problem or just normal operation. It just seems it would use more fuel than needed with it unlocking going down flat the road. It doesnt get good mpgs, but its a throttle body 350 so thats kind of expected. And it seems it would cook the tranny with it being unlocked long periods of time. Any help would be awesome.