early transmision shifting

:screwy: can someone please help . i have a 2001 astro van that shifts into lock-up very early. it almost feels like the vehicle wants to stall . the tow/haul button does not work at all. i have had it checked for transmission codes but there are none . i find myself driving in "3" instead of "D" to avercome this problem . when it does shift to early , the kickdown still works as it should .

any sugestions????

I think I have the same problem with my 98. Does yours shift back and forth from 3rd to overdrive around 40 mph?