What was changed on the motor to bump the tq up from 555 to 610?
and the hp up to 325? I would like to make some more power but I feel like Im starting with a handicap having the '03....

 

Well you are and are not handicapped. Due to the larger processing ability of the ECM on the 04.5 and up, programming changes equals more HP than the older motors... up to a point. The high HP guys are usually the 03-04 motors due to lack of 3rd injection event among other things.

The biggest difference between the two is programming. After that, mechanically you have different piston cooling oil jets, piston dome design, cam profile (03-04 is actually better), sodium filled valves, different valve seats, a little better flowing head, injection angles are different and only 5 hole instead of 8 hole...

A couple of things I am forgetting but I think are minor but am sure someone else will chime in.

I thought I was handicapped too with the silly 235 motor... and for awhile I was... but no more!

 

Thanks for the quick reply, Im looking for the best way to make a reliable 500hp.
any suggestions?

 

There are several threads on just that subject recently. Do a search and enjoy!

With that motor you will probably need small (50hp) injectors to get there along with programmers, a turbo and other mods of choice.

 

The 04.5 has a 4" elbow after the turbo, the 03 is smaller. The 04.5 also has a cat. Your 03 should get a little better fuel economy also.

 

Agree what these guys said. The turbo is smaller on the 03/04, than the 04.5-07. Then you also dont have the electronic wastegate actuator on the early trucks.

I was surprised how much better the mileage was on my 03, running TNT 5 and 9, compared to the 07 on the same levels. It was a HUGE improvement