Snapper LT16 48" mower engaging issues

[Old Snapper]

I have an old but taken care of LT16 with a new deck. I put 2 of these tractors together to make one. Service shop said to use the larger tires. I raised the deck in the back, but when I engage the mower, it may run for a few then bogs down the engine and the belt gets hot. It is worse if I raise the mower deck. I started to mow as soon as it engaged and I noticed only the middle blade mowed then turned off because of the belt. Any ideas?
It was nice finding this forum when searching online for answers.
Thanks in advance