I own a 1988 Suzuki Samurai that has over 243k miles on it. Every 4k miles I put a bottle of Prestone Complete Fuel System Cleaner, and to this day it gives me about 34MPG on the city. BTW this is my daily driver back on forth to work and believe me, the traffic to get through the gate is horrible.
Fuel additives might help a little if you us them all the time. But if the injectors are already dirty it not gonna help at all.
Cleaning the upper engine, water through the intake will work as good as anything. Pull a head off thats had a water leak and the bad hole will be very clean.
I've never used seafoam, but have been thinking about trying it. I'm a big fan of Lucas fuel system cleaner. It's is petroleum based, so you don't have to worry about pouring detergent in the tank. It works in gas or diesel.
B-G 44-K in the tank with a full tank of gas, bg makes the best in the tank fuel system cleaner, youll have to find a bg dealer to buy some, seafoam is pretty good stuff too
Marvel Mystery Oil, haven't used that stuff in awhile. Last time was on a 65 ford, it had a stuck lifter, boy did that thing smoke, eventually it cleaned it up. I put seafoam in everything, weed eaters, chainsaws, trucks, it really seems to do the trick everthing starts right up.
All I know is that Chevron came up with a fluid capable of cleaning injectors years ago and when the patent ran out everybody copied it. I am skeptical of claims about a product's superiority unless there is controlled testing.
Top tier gas has enough cleaners to keep the system clean without anything added. Check the list, if your gas station is part of the list you are good.
30K in the truck and you want to "clean" it? You must really love that truck. I wouldn't put nothing in it. http://www.toptiergas.com/