Something is clearly out of wack. Double checking the cam is where I would start. My 360 is very similar to your 340, other than the fact that I have 25 more cubes. I used to run the same 284 cam you have [ presently 285 XEHL series ] with approximately one point [ 9.7 : 1 ] less static compression and Indybrock heads. I can blow the tires off from a roll in 1st. gear. FWIW my old 284 cam was one whole tooth off when we degreed it. As near as I can recall we wound up running it at 104.5*. I run 32* total advance all in by 2,000 rpm and 18* initial. My carb is a 3310 with 68 primaries and 76 secondaries on an RPM Air Gap manifold. Good luck, it should run really well when you find & fix the problem.