questions about gearmotors

Basically, I want to ask about a motor that has the geardown built in versus a setup that involves a 'regular' motor (110v ac ,1hp , 1725 rpm for example) coupled to a geared speed reducer. My application is a rolling mill. The motor I have is 1 1/2 hp w/ 240 in. lbs. torque , about 90rpm. I have another motor (regular, as noted above) and I can get reducers cheap at surplus. I can do the math to find the reducer I want , to get the output specs I want but I'm not sure about reducers. Like, do they have specs that indicate how tough they are?... or what do I look for to be sure a given reducer will hold up to my task. I've had issues with small rolling mills breaking down , so I got a bigger one. Maight it be as simple as just getting a big-ass reducer that looks as beefy as my rolling mill. Silly way to put it, I know, but if I knew the perfect way to ask the question, I'd probably already know more of the answer. TIA, Dar