gadge used to read cold replaced sending unit and now gadge reads all the way hot ....Whats my issue

 

sounds like the wire from the sending unit is grounded. or a bad gauge, or a bad sending unit

 

Did you use tape or paste? Paste is better so the threads will ground to the manifold.

 

no tape or paste....will this make a difference....do you think the new sending unit is bad

 

tape or paste- all that does is seals the threads to keep it from leaking.
is it bad- im not sure, there are tests you can do to test it, do a search on google or get you a haynes or chilton manual, i would get one either way especially if you arent familiar with these trucks.