Have a similar problem with 4L60E in my GMC van. Rebuilt trans with a kit fromPATC. Van would move forward and backward but with drag in reverse. Band appearred to be dragging. Took out 2&4 servo kit. Reinstalled original and seems fine but no 3 or 4 unless trans connector unhooked. Then have 3rd and reverse that will spin rear wheels on stands with brakes on. Reattached connector. Shifts out of 2nd into nothing until higher speeds when either 4th or lockup comes. Have removed pan and checked solenoids- 28 ohms and click w/12 volts . Spools in valve body are free. Acumulators seem fine. Any ideas what to check next? jr

 

Just unplug it, see what you have.