700r4 problems..please help

i have a 4x4 1990 gmc suburban with the 700r4 transmission(automatic). got stuck in a deep mudhole and it got filled with water. we drove it home and it was shifting hard, after draining the transmission fluid and putting new in it with new filter it wont shift out of first gear. it goes right into reverse and 1st with no noises or anything unusual but it just wont shift past 1st gear. we have changed the fluid 3 times now(is still a little pink) and the last time added some lucas stuff to it said to get rid of moisture and smooth hard shifting. we also took the valve body out and cleaned it and changed fluid for 3rd time. we took it for a short drive and got to 2nd or maybe 3rd couldnt really tell but then stopped for a minute and then it wouldnt shift again.. anybody have any information on what we can do?  

update:
after changing the fluid about another 4times including a "transfusion" and taking the valve body out, cleaning it along with the solenoids, we now have all the gears, but need high rpm's(25-30mph but speedometer is off 5+mpg due to the 36" tires) and then it hard shifts(sorta bangs) into 2nd gear. we think problem could be one of the valves in the valve body has some scratches on it therefore maybe sticking or is stuck. i have also read about the accumualtor which has something to do with hard shifts..any ideas on what the problem may still be?  

If your's has a detent cable make sure it's adjusted right.Grab it and pull it out and let it pop back a couple of times,that should unstick it.Be very careful adjusting the detent cable.don't drive to hard till you have it right or it will burn up.I had the same problem,with the pan out you can see if the spring is working properly when pulling on the detent.Hope that helped.  

I have a chevy S10 Blazer and have the same problem same type trans but it wasn't caused by water getting into the trans. This problem happined when,I lost about half the fluid when,I got hung up on a tree stump and busted the pan. no damage to trans case or any other parts. replaced pan put in all new fluid and the thing shifted great for about ten minutes then it wouldn't shift out of 1st gear. its got a new tv cable, adjusted to specs changed fluid and filter a 2nd time still no luck at getting this thing to shift. local trans shop says to rebuild it but it's got maybe 500 miles on it anyway there going to say that this day and times. any info would be a great help on a tight budget rebuilding is almost impossible.