Speed Issue's

[Phoenix454]

I've just completed a VN 5speed conversion into another car (not a commy) . . The car "Cuts out" at 35/ 40km/h, the motor die's but then will come alive again until a similar speed, so it's kangaroo hopping down the road. Doesn't appear to matter which gear it seems to be in. I've replaced the speed sensor, 2 different memcals (Standard and Mod) but i don't have a speedo plugged in. I have a highly mod speedway memcal which has a lot of the reading stripped off it, which has the car driving like it should through the gears but rough idle and hesitation is quite bad but i want to have the car runnng on the stock chip so the problem then is fixed . . It has a VP series2 engine loom which has the 2 wire Oxy sensor and the computer is VN "series 1" . . is this a problem . . .

Thanks