Turn the wishbone around and use the double end to saddle either side of the "pumpkin".
Then use the single end forward onto your crossmember.(this speaking rebuilding the whole wishbone)
That should allow you to keep gas tank and stop the side to side wobble.
You say you were going to "originally" keep the gas tank in a stock location. Does that mean you're not anymore? If you're not, just run triangulated uppers and you're done. You could get more than enough triangulation with that setup.
Yeah i moved the gas tank to the rear of the bed, if i run triangulated uppers, would that be the link bars running from the pumpkin towards the front corners?
Yup. It'd be like the wide leg you have going towards the frame. Just another one on the other side. Or you could wishbone it from the pumpkin going forward. Then you'd have no issues.