You are going to have to remove the deck and get a good look at the drive belt and pulleys. Something is not releasing and/or worn. My guess the idler arm is not fully releasing or a bad pulley
Good Answer,I have since removed the mower deck.I checked all the moving parts,and springs,i also checked the belt adjuster nut,for proper tension prior to removing the deck. This was driving me crazy,until i got a brain storm. I went to my neighbor,and asked him if i could try the new belt on his tractor. He has the same make and model,with a 42" deck. He was kind enough to let me try this,guess what,the new belt came up short on his mower also. The new belt was supposed to be a 42" belt as stated on the package,but it was mislabeled. It Is odd that Quality Assurance,didn't check this belt prior to selling it to the merchant. I'am not sure where this belt was manufactured,if this was from China,they haven't a Quality Assurance program.What they make in China is what you get,without testing or proper labeling.Thank You,for your suggestion. Yours Truly,Brad Locke