What do you have for tire pressures and soil conditions?  What tires are on the 290? Same tread depth left as the Deere?  Bias/radial the same?  Looks like the Case is longer and even outweighs the 4955 on TractorData.com.  The 4955 has 176 drawbar hp but I can't find drawbar HP for the Case.  Tractordata doesn't have it and the Nebraska link won't open for me. I'm betting it has quite a bit more drawbar hp than the Deere as well.  I'm guessing it's a tire problem.  More weight should help but doesn't solve the real problem because the Case already outweighs the Deere (on paper, anyway).