2001 Explorer Sport O/D light flashing...

I just bought a 2001 Explorer Sport in a private deal. The truck has 50,000 miles on it and it really clean. It shifts perfectly except once in a while when shifting from 2nd to 3rd the RPM's go way up like it is slipping and then it shifts hard down into 3rd. Then it will shift fine for another 20 minutes or so untill it does it again. Every so often when the transmission does this the O/D light will start flashing. Someone told me it is a shift solenoid that needs to be replaced. Any ideas or suggestions? Is this a part I can buy and put in myself, or does the trans have to be pulled? With the low miles it has it cant be a serious trans problem can it? I hope it isnt! Thanks for any advice...

yup, it sounds like a sticking shift valve. You will need to pull the tranny and while you're at it you might as well replace the forward and reverse planatery gear sets (They are known to go) If you have never done tranny work then i don't recommend trying this yourself, its kinda a pain.