Which route would be less higher grade

I was thinking of taking I 80 over Colorado but was thinking of maybe trying I 70 but heard that Hwy 50 might also be good, so my question is how is 50 over 70? Is 50 flatter over all and are there any large ups or downs? The downs get to me as I have had some scary moments in the past even though I was doing what is right I just don't feel comfortable on a steep or long down hill. I have done the grape vine a few times and that is not bad. Toyota Trundra 5.7 and a 22ft HiLo trailer about 5000 lbs fully loaded. Would love to hear from those that know the routes.