What do you mean by check valves at the wheels? There are two check valves but they are not at the wheels. The IWE actuators are at the wheels. If he has only replaced the check valves maybe he doesn't even know the actuators are there and one if not both of those could be bad.
2012 F-150 XLT 4x4 EcoBeast SuperCrew
2007 F-150 XLT 4x4 5.4 SuperCrew - Leveling Kit - Magnaflow Cat Back - Tonneau cover - Traded
2004 F-150 4x4 S-Cab, 4.6, Auto, Edge Programmer - Traded
Everything You Wanted To Know About IWE's