Rutex offer some drives that run upto 40Amp motors, but they are twice the price of the geckos. You must be planning one big machine to want 1500 oz/in?!
edit - just a thought, if you could run them at 20Amp, losing half the torque, you could run them on a reduction pulley, halving their speed, but boosting your torque back up. Obviously you'd need to go for a course ballscrew to regain the speed loss.