Thanks for the comments, hmm lets see..
1. The seats. No, adding the seats created zero instability. 2 points though. I had a light duty 12 once where adding the seats did make it a bit tipsy. I had 15 inch pedestals but when I changed them to 7", it was much better. However, this boat has an unusually wide beam. Extremely stable for a jon boat.
2. The herculiner on the bottom does create drag but this boat is used in a t/m only lake. There is an equation where you can see the max possible speed of your boat without getting it on plane and for my boat, it's 4.2 miles an hour so w/a 55 lb thrust motor, I get the 4mph out of it no prob. any larger of a t/m and I'll just be pushing more water till on plane.
The pic below is the old light duty w/ the higher pedestals. THis boat is a no-no. Lower pedestals were a must. This boat was like riding a skateboard on ice.