RMAX,
The Juice is the power upgrade that I bought after a lot of research. There are others that folks here also like. You can do some looking at edgeproducts.com.
The OEM guages do not measure the temperature of the exhaust. When you add a power box or chip you need to do that because more power makes more heat. You do not want to exceed (lots of discussion on this, but I think --) 1300 degrees if you are measuring at the exhaust manifold. I did not exceed that on my way to Utah, even on 8% grades, though I did see 1275 a couple of times. When you buy a guage, like the SPA Digital which is the one I bought (available from Kennedydiesel.com and others) you must tap into the exhaust manifold to insert the temp. probe. It sounds hard but isn't. Kennedy can walk you through it or any competent mechanic can do it for you.
This is the single best upgrade you can do if you tow heavy. A 4" exhaust helps move the heat out faster and is another good idea in my opinion.
Regards and good RVing.
Bob