I have a forestriver berkshire with the isb 340hp cummins is there anyway to boost the power without void of warranty.

Yes there is a way to upgrade horsepower, and keep your warranty. You will have to go to cummins or a cummins repair facility. Once they plug into you engine they can give your options for horsepower and torque. Depending on cpl, and engine family you may be able to just program engine to high specs. If your engine is at the max for its family you would need to change hard parts, poss injectors turbo or other things. If its just a program, you will need to fill out a engine/warranty form to cover the modification usually has a 500 dollar charge plus what the dealer charges for programing the ecm, and a calibration password. My shop usually charges around 900 for all with the warranty uprate. Also be aware if you could get your specs on the trans so you and the dealer can safely decide what's best.