Spn1347 fmi16 / p0094 on mx13

Hello guys. I've been getting spn1347/p0094 on my mx13. If I'm bobtailing truck runs like I just bought it. As soon as I hook up a trailer and get on the gas good the stop engine light comes on and throws this code. Then the stop engine light goes away after a few seconds. And keeps doing this until mil light comes and stays on.ive changed both filters. Changed fuel pressure sensor fuel rail sensor and pressure relief valve. Also pulled control valve out the back and checked for tears in the orings. I unplugged each unit pump and drove the truck and it runs on both unit pumps. At idle my fuel pressure has been reading 65psi. I cleaned out hand primer filter sieve and got it up to about 78psi but it went back down after a few drives. I've put clear hose on the fuel filter return and noticed a lot of bubbles in the fuel. Truck runs fine until I get loaded and pull a hill then It struggles. Any advice would be appreciated. Thanks