What engine and what is your current HP? Most engines can be turned up to 250 via laptop with the right software. Keep in mind what tranns you have, it may not be able to tolerate more power!
The engine is a 3126 cat in a freightliner. I have a SCT programer for my pickup and u cane go from mild to wild from the same box. Almost forgot the cat is like 190 hp not much for pulling hills.
What year is it? I had some ~2000 Ford F750s with Cats that were underporwered. I don't remember the rating. The Cat dealer was able to reprogram them to add a bunch of torque but not much HP. Adding HP would have required new turbo, etc. ANyway, my drivers were very happy with the change. As Thomasbus24 mentions, Cat said I first had to check with Allison to make sure my transmissions would be OK with the change before they would do it.