1997 4l60e intermittent 3rd gear shift

[mikey1994]

hello, having an issue with 3rd gear. trans has about 1,000 miles on it. truck will sit and idle for 30 minutes and will drive fine and go through all the gears and go into lock up without an issue. when trans shifts it shifts very well. seems to mess up when i come to a complete stop and take off. first and second shift as they should but 3rd acts as if its slipping really bad. if i left off the throttle it goes up the road but can feel it slipping. not sure if this would be the 3rd and 4th clutches going bad or a possible valve body issue. any help or suggestions to try and figure out this issue would be greatly appreciated. thank you.