well heres the problem , my tranny's acting up on 1st to 2nd . when it's in 1st and rpms get to about 3500 i can feel it slipping ,then it will shift into second and keep slipping till rpms come up then goes into gear, 3rd and 4th work just fine . any ideas of what might be causing this other than it being a 4l60e? thanx in advance