Not sure what to do with my current heavy mauler lance.
You absolutely need to get the Flashman out of it. As marvelous of a 'Mech as it is, it's a cavalry, and ill-suited for the lance as a whole. I'd really suggest dumping the Catapult as well, it's not the strongest brawler out there, and there's better ways to get plasma rifles in the field.
Both the Victor and the Yu Huang are great suggestions.
In the case of the Victor, it's that it is wholly dependent on it's single, massive weapon. You'll probably never lose the 'Mech, but a single critical hit to the right arm will pretty much put it out of the fight.
The Y-H9G or Y-H9GB Yu Huang can both be stellar urban brawlers, provided you don't decide to go blow for blow with some standard engined 95 ton zombie like a Banshee. The LRM-10 doesn't seem to jive too well with the other weapons, but it can throw in with the ER PPC on straightaways and fire indirectly at opponents out of LOS or drop mines to cut off escape routes. Worse comes to worse, you could go with the new Big MAC refit with dual MML-7s and dual Plasma Rifles.
My suggestions? Get an Emperor, a Berzerker C3, or both. Despite the XL engine, the Emperor has proven itself time and again for me as an absolute tank and powerful utility player. Four big guns gives it firepower few 'Mechs can match outside of 9 hexes, and dual LB-10X gives it a lot of crit-seeking potential. The Berzerker, on the other hand, is just plain 100 tons of TSM mean in it's C3 configuration.