I have a 2003 Ford Explorer 170000 miles. While driving, either slow or highway if feels like I am going over bumps, like crossing a cattle gap very fast. Is this the transmission and how can I fix the problem?

Have you ever had the tranny fluid replaced? My Jeep was doing something similar to your Explorer and when I had the tranny fluid changed it acted like a new vehicle even though it had 175K on it. Worth a shot and probably needs changed anyway. My Jeep was shifting hard even though it's an automatic. Once fluid was changed it shifted smoothly and I never knew it unless I looked at the tach meter for confirmation.

Make sure the transmission dipstick shows full when the truck is HOT, parked and engine idling. If the 2003 Ford Explorer still slips, I'd have the transmission pan removed by the Ford Dealer and let their transmission technician see what debris is in the pan. Have them change the filter and hope for the best. It's worth the money unless your positively sure the transmission can't be fixed easily without replacing it. Then, if you want to keep the vehicle for 5 years or more, have a new remanufactured Ford.