The losi HT pipe is a great pipe and can usually be found on ebay for $25 or so shipped.
Swapping the wheels/tires out for some smaller/lighter ones will make it much more responsive. Then you will either need to do the gear flip mod or get the +1 CB that losi sells.
Those tires are power suckers. Lots of rotational mass.
With t-maxx 2.5 chevrons on mine with the gear flip mod, I could run neck and neck with an LST2.
If you get a better engine, you may need to upgrade the two speed assembly to LST/LST2 version or you will have issues due to how weak the AS version is.
The losi mach 427 gold head (stock LST2 engine) is a pretty good bang for your buck engine. The Losi 427 green/grey head has a bit more pep than the gold head version as well.
Or you can go nuts and get a LRP28S3, LRP30S2 or a picco 28... but then you would definitely need to upgrade the two speed assembly.
Replaceing the stock clutch shoes/springs with
HPI teflon savage shoes/springs will make a world of difference off the line. They engage earlier which makes it easier to finesse the truck around.