Pull codes, see if you have a P0751 set. Even though this notice is for 2010 vehicles
http://www.revbase.com/BBBMotor/TSb/DownloadPdf?id=171494
TSB 10-9-9
2010 Ford Taurus 6F50/ 6F55 Transmission—Dtc P0751—Harsh Or No Forward Engagements
FORD: 2010 Taurus, Ford Edge, Ford Flex ISSUE Some 2010 model year Taurus, Flex, MKS, MKT, Edge, MKX vehicles equipped with 6F50/55 transmissions may exhibit DTC P0751 and delayed/harsh or no forward engagements and/or slipping 6-4 or 5-4 downshifts. This may be due to a broken orifice restrictor cup plug in the forward clutch circuit. Affected transmission build dates are 12/11/2009-04/15/2010. The orifice restrictor cup plug sits in the transmission case below the forward clutch feed seal under the main control valve body. ACTION Follow the Service Procedure steps to correct the condition. SERVICE PROCEDURE 1. Remove the main control valve body, refer to the Workshop Manual (WSM), Section 307-01. 2. Remove the forward clutch seal. See WSM, Section 307-01 for additional information. 3. Inspect for a broken orifice restrictor cup plug in the forward clutch circuit. a. If no damage is found, continue with normal diagnostic; do not continue with this procedure. b. If orifice restrictor cup plug is broken, continue to Step 4. 4. Remove the transaxle, refer to the WSM, Section 307-01. 5. Disassemble the transaxle, refer to the WSM, Section 307-01. a. Do not remove the bearing cups or seals from the transmission case as the case is to be replaced. b. Do not remove bearings from transfer gear shaft or differential. 6. Inspect the forward clutch piston for damage. Also, look for a small round piece of metal in the clutch area. 7. Replace the transmission case half, clean and reseal transmission. 8. Reassemble the transaxle, refer to the WSM, Section 307-01. 9. Reinstall the transaxle, refer to the WSM, Section 307-01.
Could be related to the symptoms during your test drive. Lurching/clunking. More than likely a combination of valve body (affects line pressures), broken orifice cup and TSS/OSS sensors.
Also, what fuel are you running? See if running premium instead of regular makes a difference. You may have to try multiple brands also, always from a busy station to make sure the gasoline isn't getting stale.
