Im working on a c50bx ps serial number 58257A k21 with a lpg nikki vaporizer

Im the second tech to look at this issue. This unit is surging at 3/4 to full throttle. Last tech swapped vap, both injectors, maf sensor, throttle body and governor. I pulled codes found a p0500 wheel speed sensor code. I blocked the unit found that wheels moving sensor is not reading. I found similar issue on other discussions here but no solutions. Thanks