I Start my engines and in 3-4 min the engine stumbles and check engine light comes on.
Scan engine and get crankshaft position reference error. Change crank sensor and same problem.
Shut engine off and restart warm and seems to be ok.

Any ideas would be helpful Thanks

It sounds like a bad connection or bad ground. Have you cleaned the grounds at the rear of rhe intake manifold on the passenger side? The grounds are very important on these.
Take a minute to fill out your signature so we know what you are working on. It's under user cp on the top of the page.

or in my signature you can also find the link. as well as the checklist you should fill out and submit back to us in this thread.

Have cleaned all ground and also upgraded PDM and still problem

Have you check the voltage on the wires that go to the crank sensor? What kind of truck do you even have? Need to fill out signature so we know what youre working with. The checklist would also be good.

Using digital multimeter....If you pull the harness off with the IGN ON engine OFF there should be 5V on pin C grey wire. The Black wire to pin B should be Ground.

If that checks out then when you get it in idle with the sensor hooked up, probe into the insulation and you should still get the 5V on the grey wire and the yellow wire should have 4.5V on it.