Well, stepping up to a Grand L like the 5460 or 6060 is another story -- those would be a significant jump in capability (and size and cost too, so be prepared to handle a bigger tractor and get a bigger chunk taken out of your wallet). Keep in mind however, that some of the added power is going to be offset by the added weight on a hill situation. In fact, my previous lightweight B with 29HP was significantly more of a hot rod on hills than my heavier L with 32HP for this reason. That is probably why the dealer is jumping over the smaller L / Grand L models and pushing you towards the 5460 and 6060. They would have some additional oomph to overcome the added weight. Still, in terms of power to weight, the
B3350 is quite a hot rod compared to other Kubotas. Before making any decisions, do calculate power/weight ratio for other tractors you're looking at, as this is probably the best indicator of power on hills.
What gear are you operating in? Are you running the engine at high enough RPM? Are you using the HST correctly? A lot of new users treat the HST treadle it like a throttle pedal, and think that pressing harder makes more power. But it's the opposite -- pressing power means higher gearing, so it's worse. On hills you need to increase the hand throttle and back off the HST treadle to find the right combination. And of course choose the correct gear (medium for sure, and possibly low).
I suspect your problem may be a matter of proper HST operation, as the
B3350 should have plenty of power for its weight.