C&L 76mm maf problem

[5150coupe]

I just recently installed a 76mm maf to replace the stock and the car runs bad. Drove it for two days and it still isn't running well. It stalls out at slow speeds and I lost all top end power. What make it strange is that my friends 76mm C&L works fine and both of our sensors are configured for 19lb injectors. My sensor is ok because it works fine once I put it back in the stock maf. The only difference is that when I used my friends C&L setup we used the stock air box and now I am using a large K&N cone filter. Could the use of the cone filter make a difference? What else could be an issue?