99 Dodge diesel VP44 on the way out?

I replaced my VP44 injector pump about 2.5 years ago, but didn’t replace the lift pump. I know this was dumb, but the first injector pump died because of unwinterized fuel in -15 weather. The truck was fine for a while, but started stalling for a split second when I give it a normal amount of throttle. The check engine light comes on, but goes off after a few starting cycles. Repeat process. Now I just give it throttle to accelerate at barely over idle and keep it to surface streets at about 35. I put in a new lift pump and pressure gauge. Fuel pressure is fine, but it’s still doing the stall routine. A code reader won’t connect for unknown reasons and I can’t bring myself to spend the $1k+ for a new injector pump until I’m sure that’s what’s going on. I’m tempted to just take it on the interstate and see if 70 mph kills it. Ensue fun towing experience. Could something else be causing this or am I about to spend the money for the pump to resolve the issue?