Why does my Mountaineer shutter?

Feeling like "rumble strips" is a common symptom when there is a torque converter (of the automatic transmission) engagement issue. The torque converter clutch fails to engage properly and a rumble occurs. This should be somewhere between 25 and 40 miles per hour typically. Can you describe when the concern happens? The first thing to be done is to replace all the transmission fluid -- something that takes an effort on this 5R55 transmission.There is a drain plug and fill plug, and a fluid injection tool is needed, unless complex exchange equipment with capability of heating the fluid Is used. If fluid change doesn't help (even twice), torque converter replacement may be needed, as well as other testing. www.repairpal.com/repair-shops