it stumbles taking off, and surges before it shifts, i read in the manual it even states that you will experience this if the egr is bad or missing, if i hold the gas and brake,, it wont even spin the tires, it goes to about 1500 r.p.m and bogs down ,,,suggestions, advance the timing? cat stopped up, or just go back factory setup? i dont want to spend a fortune on this???