Based on our shop experience specializing in heavy-duty brakes since 1985:

• Bench Bleeding: Never skip bench bleeding the master cylinder assembly on a vice before mounting to the firewall or booster face. Trapped air pockets inside the bores create persistent spongey pedal issues.
• Vacuum Routing: Ensure your vacuum supply line is routed cleanly without kinking to maintain required assist levels at idle for safe heavy fleet stopping.
• Fluid Compatibility: Use clean DOT 3 or DOT 4 brake fluid only.