I just bought a 03 f150 that has around 173k miles on it. The transmission will kind of vibrate or yank the truck when going around 30-45 mph and then letting off and hitting the gas again. I’ve checked the trans fluid and replaced it because it smelt burnt and it was dark brown. I don’t know if it could be anything else because it’s only done it once ever since I changed the fluid. The motor also has a small ticking sound that is coming from the engine. I noticed that after I changed the oil to a lighter weight it got louder and ran worst, so I changed the oil back and it ran better and wasn’t as loud. It also tends to go away once the motor has warmed up. Does anybody know what that may be ? I’ve changed the spark plugs, oil, trans fluid and I’ve also did the sea foam method with a vacuum hose and gas. 5.4 liter, 4x4.

 

The motor also has a small ticking sound that is coming from the engine. I noticed that after I changed the oil to a lighter weight it got louder and ran worst, so I changed the oil back and it ran better and wasn’t as loud.:

Check and see if it is coming from the front around the timing chain cover. (Without hurting your hand, (Be real careful here with the truck running) place it on the v cover almost the top of the cover just below where the valve covers fit overs on both sides. You will fill the chain and stuff slap if they are going bad.) A lot of times that is a tensioner going out or the guilds worn through letting the chain slap as the tensioners can't hold the chain tight. (Weak spring in tensioner as the oil is what holds it tight/guilds for chain worn though that allow slack in chain no matter what the tensioner does and you hear the chain making a clicking/ticking sound.) That would be my first guess as I am not there to hear or see. If everything else is running well.