I have a 2006 Ford F150 with 213,000 miles. From 40-50 MPH under light acceleration it feels like the trani/rear end slips and it sounds like knocking. Before it would make a rattling noise around the same speed (Especially going uphill), and now it's slipping. No engine light is on. I did some research and found out it could be my spark plugs misfiring. If anyone knows anything about this let me know , thanks!

 

Spark plugs and/or coils.

 

See if there are any codes, even if there is no CEL lit.