How to get heat gauge on track

1995 dodge ram 1500 318 auto 2wd short box sport. i recently had a goodyear put in a thermostat and both temp sending units. they had issues with it running upwards of 230 by the gauge, so they tested the actaul temp with a diagnostic check and it said 198 degrees. so they kept my truck another day and swaped out one of the sending units. they called and said its done and good to go. iwent and paid and picked it up the gauge is around 210 degrees and i called them when i got home. they said it was good here,and you were in stop and go traffic on a hot day. thanks for calling… but if you want to take this a step further, let us know… ? am i missing something? im not happy. it came in reading 201- 205 now its 210 ish. im mechanically incline and wanting to know what to look at on the truck to fix the miss reading/ or hot condition.

Factory gauges are notoriously unreliable.

I would recommend rather than paying attention to the exact numbers on the gauge that you pay attention to any abnormal fluctuations that might indicate problems.

Of course you can always install an aftermarket temp gauge.