explorer trans problem

I have a 1996 Ford Explorer 56,000 miles 4wd 4.0 engine, with an intermittent transmission problem. On occasion when driving at low speed ( under 10 mph) and coasting, when I go to accelerate the trans slips, then goes into gear. This will happen 3 times in 1 day or once in three months. Hard to duplicate problem. Been to several shops all tell me it is an electrical problem, but cannot fix it. Also on cold mornings there is a delay when going from Park to Drive. If you have any advise please help.

Thanks

The transmission is ready to go out.
Has the fluid been changed?
Even though your miles are low, the fluid deteriorates over time.

Trans was rebuilt about 1 year ago, guy who rebuit it is giving me the stroke job, Been back to the shop 4 times already. says they cant find the problem.thinks its eletrical, but this didnt happen until the trans was changed