I'm a very experienced (multi championship) driver with a perfectly tuned kart/engine and on certain tracks I'm off by 6 sec a lap because of aero drag. Some things you can't do nothing about like being big and tall. On tracks with short straights I can win be it's still a challenge because of high vertical weight.
1-1/4" axle is a good axle. If you have a fairly modern kart with a basic set up, that's all you need.
When I hear a rookie say he's loose, first thing I think is driving technique. Snap oversteer: You go into the turn too shallow and fast then try to turn all at once 2/3's the way through and the back end steps out killing your speed. Slow down a little, go in as wide as you can, keep the steering wheel steady and drive a perfect radius without slipping the tires and you will come off the turn fast and be faster on the straight.
Sundog