1997 Gmc Sierra Not Working Properly

[farmboyont]

305-4l60E Ok this has been going on for a couple months. The truck was working great. It would shift into 4th just like normal and at the proper operating temp it would lock up. The earliest it would lock up was about 60 km/h ( Reads about 70 on the speedo) but only with the proper operating temp. I had been drivig it like a granny for the mileage thing but was only getting about 10 mpg. so one day i really had to drive it hard and the mileage went way up. Tested mileage on a 700 mile trip and with stuff in the bed(matress,dresser, etc. with a tarp over it it maxed out about 21.5 mpcdn.g (about 18 American). So of course I was really happy with the truck. About Nov. when it started getting cold it started to lock up as soon as it could. For a while (2-3wks)that was how it was working(every once in a while it would work normal) then it started to get to the point that it wouldn't unlock at corners and stall the truck or come close to it. ((1)) It would also shift hard at every shift and was/is shifting as soon as it possibly can.WHe before it was shifting into forth at 70 (on the Speedo) it is now shifting at 50 or less. When it shifts, like i mentioned it was hard but not hard like a clean crisp shift but as soon as it could at way to low of rpm so it would kinda rock(best i can describe it) I hauled a 16' livestock trailer with it and it started to work a bit better, good shifts was unlocking a bit better, etc. Worked a bit better even without hauling it after that. But now it's back to what it was doing only worse. Now it locks up in every gear (including reverse) when I back out of the lane I have to put it in N to get it to stop without stalling or coming close to it. Down to road it works great, have no complaints. If I go 100 km/h for 10 miles it unlocks better when i stop but if I have to stop a mile after that it won't unlock right . Now it also has two new things to add to all this. Sometimes when you go to take off it does not want to go, it will move all of 5 km/h and want to stall the whole time it will be very stuttery. turn the key off and on quick, away we go(still with shift problems). Just to test it I put it in neutral right after it did this( did not turn key on and off) and the engine acts perfect, no problems at all. When your driving in the yard/drive way it will just cut out for a half second and come back. Radio turns off and everything, and comes right back on. The one time it actually didn't come back. When it stalls at corners and the time in the yard it starts right back up. the abs will also randomly start going off. You can hear it cycling mostly when coming up to a corner of just after you used the brakes. Every once and a while you'll need the brakes when it's cycling pointlessly and will lock you from using them. press on the pedal but it won't do anything except slow it slightly. The one time at an intersection (side road and bigger highway) it did this and I pushed it tilled it worked and it stalled the truck and took atleast 20 cranks to get it going again. I should add that after that 2-3 wk period mentioned above if you come to a stop sign/stop and it is slippery and you're traveling below about 25 km/h, if the abs goes off it will stall the truck. Not sure if it cuts out immediately before the abs goes off or when the abs goes off.? Where the ((1)) is above a replaced the fuel pump somewhere in there. Broke the fuel level float while doing so. Right after replacing the pump when going down the highway it you were going up a hill or whatever(when it would shift to 3rd) it would lose power and the harder you pressed the gas the less power it had. If you let up you would have more power but the only way to get back to normal would be to turn the key on and off quick and it had full power again. It would do this once per trip or not at all but once or twice it did it 3-4 times. It did this for about 3 weeks but hasn't done it since(2+ months ago maybe it got replaced) The truck started the initial problem just slightly before this. Sorry for this stupidly long write up but this truck is driving me crazy and want to gave you all as much detail as possible. I love driving the truck but am going to have to pull it off the road and drive a GMC Safari till i can get it fixed. Should also mention that for the last month 2nd gear has been weak with higher temps and speeds. If you go to pass someone and have to shift into 2nd it -slips- like crazy. The truck has an aftermarket cooler on it. Not really sure if -slips- is the right word. Just what it seems to be doing. The computer throws codes -engine light- once and a while but they never stick around for long. Can't really afford to put a bunch of money into the truck cause it ain't worth a whole lot. A gate got in it's way one day so the front bumper is dented up a bit as well as the right fender dented. all knowledge on this is greatly appreciated.