?Thermocouples need replacing

?Thermocouple problem. Removing them out of the loop appears to fix the problem of worsening & persistent shutdown after short distances on a slope or grassy terrain (goes well on flat).
They are screwed onto the frame 2 inline with 2connection screw posts each for + & - lead connection .
Run with 2 x 12V batteries currently using 55AH, though the machine is supposed to be able to use 38 or 55AH with no mention of any change-outs.
No part numbers, but the sheet metal plate inside reads (P?)A223-40. Anyone know where replacements might be obtained??

thanks.