If it's reliable I'd keep it. You can buy a newer rig and end up with a lemon and be sore. I can't speak to the power. Perhaps a Banks kit would get you where you want to be. Me, I'm just not in a hurry and I don't mind kicking up the RPMs to climb a mountain. I pulled my Harley behind my old rig but, it had the GM 454. It did just fine as far as power goes. I understand that the V-10s were built to get their power at higher RPMs.
Really, it comes down to what you want to do. Me, if I knew the one I had was trustworthy I'd stick to it. I have known a few folks that bought new/newer and ended up mad because the one they traded was good and the one they got was a tub..