They will not give you alot of gains by themselves, however when designing an exhaust system for you truck you must also take into consideration what you plan on using you truck for, for example if you are an everyday enthusiast who just does mainly the big 3 "Cold Air Intake, Programmer, and Muffler" you would not really benefit from a hi flow cat.
Now we take it one step farther and we do the big 4 "Cold Air Intake, Programmer, Muffler and Complete exhaust(headers, midpipe, y pipe, muffler) you still probably would not benefit from hi flow cats.
Now when you start talking about the big 4, cam, heads, and forced induction I would recommend hi flow cats.
OR if you factory cats need to be replaced I would recommend hi flow cats as they are a fraction of the cost
I hope this information helps.
Discount Auto Performance