My BIL tows with his automatic... . hes got a 35 ft 5er that goes about 12K lbs. . He found that he couldn't keep the transmission oil temperature down to a safe level pulling the hills in the Pacific Northwest... . He added the extended pan with a large filter, which added I think 4 additional quarts of oil and that brought the temperature to a level he was happy with...
So I guess I'm saying that if you tow, yes you need a gauge, if you don't tow I'm guessing you'll never need it...
I own 3 trucks with sticks... . we have 240K miles on the 04 towing all the time and have never considered a fuel pressure gauge... .