I personally believe vacuum secondary's are for lighter vehicles. If you have one on a truck I believe it will run poor. You need a good DP carb and I'd be going up in jets to start. I believe your truck runs bad because it's starved for fuel. My 10 to 1 360 with a 509 and a 750 DP didn't run very good until I started increasing the jets and squirters. I can't remember what they were but they were far from stock and every time I went bigger it run better and better.