I have a 2005 2500 silverado hd.
Reduced engine power keeps putting me in limp mode code reads
P0135. Can any offer advice

 

Do a search here on this Forum, there's a LOT of info on this subject.
Unfortunately (since this has happened to me to) I haven't been able to come up with any single thing that works better than another.

One thing I have noticed though, that most fixes among other things, include the checking/cleaning the Grounds.

Have you encountered your Rev Limiter yet ?
(this is in no way associated with the Reduced Power situation)