I want to replace my 8N with another used tractor. The reason is that when I pull my spring tine harrow with 13 Danish Sweeps I get bogged down if I go 6 or 8 inches deep. I thought I needed 4 wheel drive and a little more HP. I ran it this morning and my problem seems to be spinning the back wheels especially if the ground is moist. I did not stall the engine. I thought I needed 4 wheel drive at around the same HP. Now I'm not sure if I would be better off with a bigger heavier tractor with more HP or a 4 wheel drive with about the same HP. Any ideas?