What spur do you have? Steel or plastic? What gearing/tires do you have?
I had the same issue with my savage after the LRP28S3 broke in. I had to gear it low so the slipper wouldn't slip when it shifted into second. The slipper would slip with the plastic spurs and melt the back out before I noticed it. Once it slipped once, it was done. I ended up getting an HPI steel spur, OFNA hardened bell and made sure to rough up the slipper washer and slipper pad during install. Then I pretty much just tightened the nut down until the spring was fully compressed. I was able to gear it taller than with the plastic spurs.
I'm running a plastic spur now, with some proline badlands tires & wheels. If I tighten the nut all the way down it will make for about one or two passes then it's slipping again. I got a three speed on the xl but like yours it seems to be messing up going into 2nd
I'm running a stock 2-speed trans with BP diffs with traxxas 3.8" chevrons on it and 47/16 gearing now. Has been working great for quite a while, probably about a gallon of fuel.