When on the throttle the truck shakes at 45mph , but when under or above 45mph it doesn't shake , if you let off the throttle the shaking stops . I am thinking that my torqe converter is going bad . I was wondering if anyone else had this issue ? Note also that the tires are all recently balanced and it did not change anything . My front end parts are all new also . Thanks for your time !

 

It has nothing to do with the torqe converter, Read this post.

Believe it or not. most of the time it is because of a bad front shock if everything has been replaced on the front end.

https://www.ford-trucks.com/forums/1...n-driving.html

https://www.ford-trucks.com/forums/1...d-shaking.html

 

Respectfully, I beg to differ with sand-fiend (based on the information provided by the OP). The fact that you only have the vibration under engine load is what says it is a drive line issue. However, it is most likely NOT your torque converter.

I had the EXACT same conditions, and it turned out to be the drive shaft carrier bearing (also called a "center support bearing"). Get under the truck and see if you can physically move the driver shaft up and down inside the carrier bearing. If you have vertical movement, that's your culprit.

If it is the problem (as I suspect it is), you should also be aware that the carrier bearing is pressed onto your drive shaft and the retaining nut is installed with 300 ft-lbs of torque. After removing the rear drive shaft, I could not budge the retaining nut in my garage, so I took mine to a drive shaft shop where they had the old bearing off and the new one back on in 10 minutes. It only cost me $25 for them to do the work. ALSO, and this is IMPORTANT, if you remove your drive shaft, mark both drive shafts on one side only so that when you re-install the drive shaft you do not get it in 180 degrees out of phase... that will also result in additional vibration.

FINALLY... if you remove your drive shaft... PLEASE make sure to use wheel chocks to prevent the vehicle from rolling with you under it. I forgot to use my chocks when I went back under the truck to rotate the drive shaft 180 degrees (because i had NOT marked it prior to removal), and the absence of wheel chocks nearly cost me my life. I ended up with both bones in my left ankle broken which required surgery, and I was off work for 6 weeks!! USE CHOCKS!!

 

I'm also going to disagree with the shock thing. Leaf springs don't really care that much about shock condition. Other than handling like a three legged elephant, my truck doesn't ride any different with the shocks removed.The truck in that post had coils.

I'm going to throw in possible bad injector. At 45 the TC just locked and your in high gear at low rpm. This makes slight power differences between the cylinders very noticeable. I had two bad and they only showed their self at 40-45 in od with the TC locked and at the first start of the as a lack of power for first few miles.