As hmknightnc stated there are several "lucky" folks including myself
Believe I have 4 or 5 of the repaired WFCO's in operation around the shop and Rig's all easily go into boost when called for. If you are feeling really energetic you can (difficulty depends on specific model) add a remote as I did for my 75amp WFCO. Makes it easy to manually force it into any mode for any duration desired.
The easiest fix to get into Boost is a larger cable which is a lot less expensive than buying a new converter.
A 55amp converter working and wired properly with batteries in good but somewhat discharged state should get you a reading at the batteries in the low to mid 14's in less than 10 minutes. My guess you have a wiring issue, suggest you measure the voltage loss you might be surprised to see as much as a full volt with a small/long wire run.
If you decide to scrap the WFCO I would be happy to pay shipping costs to get it here.