Will a Superchip or similar mod. alone have noticable performance gains, ( for towing) in a 8.1 w/Allison trans. & 410's or should other changes be done also. etc. exhaust-intake?

There are several ways to reprogram the ECM in a 8.1 GM truck, (Westers
and Hypertech to name a few) and yes it does respond quite nicely to it
too!

Westers Programming If your not tearin into the motor.


Or modding the motor go with Hptuner or LS1edit, do it yourself, or find a good and trusted tune shop.


Superchips or Hypertech 3 if you like throwing money away.


Also good air intake, helps this motor become responsive. and depends on your budget for this motor. Few nice things out there for this motor.
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Can't speak for Superchips but I would not call Hypertech "throwing
your money away" as though the returns are less it allows you to easily
adjust for axle ratio and tire size in 1/4" steps and get your speedo
dead on if you want (I have mine tweaked to be doing 59.8 at a 60
indicated as verfied by GPS) and it does not "marry" itself to VIN like
Westers does. (you cannot uninstall and resell it) You can uninstall
Hypertech when you sell truck and resell it and not be locked into that
brand. I got mine off of E-bay used for $125 from someone that
sold their truck and it works as it was designed.At $500 a crack for
Westers (last I heard) it is to steep for my blood to justify its
returns and VIN marriage to boot. If you buy a Westers and if you sell
the truck, you either give it away with the truck or get credit on a
new wester product for a different truck, that money is "gone" in my
book.