I just got my 03 fx4 with the 4.6. On take off it feels like somethings in the bed and slides back and hits the tailgate kind of stumble. When i stop it feels like it slides back forward and hit the cab. Nothings back there it makes just a slight thud and the only thing i can think of is drive terrain?

Also on a diff problem it feels sluggish and feels like it doesnt have the power to make up a hill without shifting to third and no take off. Thought it was normal cause its got 35 m/t on it and just used to a soupd up f250 but now thinking its not normal for it to be sluggish. No codes, no misses, was told it could be a coil pack but figured itd throw a code. Please help i need to get this reliable and cost effective cause the 250 and jeep have drained me. Thanks and learning a lot from the site

 

That's not much to go on. More info might help.

 

I dont know how else to explain it the clunk only does it when you stop and when you take off. Doesnt do it turning. All ball joints are new. It feels like its in the center or rear part of the truck. Not brakes theyre brand new. You cant really hear it you just feel it.

The power issue is as stated it just feels like its lacking power. If i go up a 10 degree hill it shifts down. I can floor it and it just slowly builds speed. Theres no vac leakes cause just had it checked out yesterday. Does a lot of shifting from od to 4th on trips, take offs and passing speeds are slow, not really much else to explain. Just feels sluggish

 

Any "popping" noises on accel? I'm thinking plugged cats. As for your thunking feeling....check transmission mount for play. Also check u-joints and exhaust hangers.

 

No no popping. It literally feels like something is sliding around in the bed i try to hear a noise but cant if it did itd make it easier to locate. Ill check those things