2002 Ford Explorer

I had my oil and oil filter changed along with my spark plugs and wires one day and the next day my vehicle started acting strange. When I would take off it would delay shifting when it got somewhere between second and third gear. And after doing that several times the overdrive light would come on and start flashing real fast. But, after I got it to shift it would do just fine as long as I didn't have to stop and take off a bunch of times. I figured out that you could not check the transmission fluid because it does not have a dipstick for that. Do you think there is a possibility that when the oil was changed the person might have pulled the plug to the tansmission instead the plug to the oil since they are so close to each other and they werent sure what they were doing.