40 to 45 is when the TC locks. When this occurs, there is a 100% mechanical connection between the engine and transmission therefore, a vibration in the engine will transmit directly through the drivetrain and truck in whole.

My truck experienced an annoying vibration like this and in my case, it turned out a new IPR valve solved the problem completely. This was after having a few thing looked at.

 

I would drop the tank and check the plastic pickup foot which is a well known failure point (crumbles completely) for our age vehicles. I've been through two of those episodes on two different 7.3 vehicles, both crumbled at about the 12 year mark. It's age, and not mileage which dictates this demise for that plastic part, so your truck is an excellent candidate for needing to replace it.

Cost... not much... only about $36-40 at either

a) Diesel Orings > FORD Fuel Tank Pickup Foot Original Equipment, or

b) Riffraff Diesel > Fuel Tank Pickup Foot and Screen - Ford 7.3L Powerstroke (94-03)

 

when it started shaking would it lose power and clear up when you let off the accelerator?

 

No it wouldn't. It would shake until about 50mph but not lose power. Sorry if I missed that part.

 

I agree with what Pete said, especially if it happens with a full tank as well. It can also be clogged screens in the tank as well. More speed/load requires more fuel. If you go past the "point of no return" as far as fuel demand is concerned it will exhibit your symptoms. Not to say that this is you specific problem but a good place to start looking.

 

You know, I had the exact same symptoms last year when my stocker fuel pump finally decided to start laying down on me. All I did was replace the pump and she runs like she used to again. Just another way that fuel flow can be interrupted... a very tired pump just can't keep up with demands.

 

I agree with checking tires. Inspect complete driveshaft assembly as well.

 

yeah I should have changed everything before I even drove it, especially after sitting for a year or more my maw maw would go out and start it every few months though so it's not like the fuel hadn't been cycled

 

Maybe I missed it, but is your original complaint a power issue (at a certain RPM range under load) or a vibration issue (trans gear / driveline speed / wheel speed)? The one thing that you will find more helpful than anything else is logging data while your problem is happening. Torque Pro and/or Forscan (here's one link) will get you hard data you can share and that will help us point you in the right direction.

 

thats what I don't know. I need to scan it I know I'm just gonna start going through and looking for a scanner I feel like the shaking is bogging my engine down cuz when it does shake I lose power. I did just flush my tranny and changed the filter and gasket and it really hasn't done it since then but sometimes it feels like it's gonna do it again but it hasn't except once when I was cycling the new fluid