Do I need a new EGT guage?

[Radshooter]

My DiPricol guage sticks around 425 when the turbo is cooling down. If I wait a few minutes and tap the guage, it will drop to 375 nor 350. It only seems to stick when cooling down. When driving and coasting down hills, it will drop to 250 to 300 on it's own without tapping. Haven't had the trailer hooked up for a few months, so don't know if it works on the upper end. It worked fine last time I towed with it. This all started a couple months ago. Any ideas? Is it still trustworthy or should I replace it? It is about 2 years old.

Thanks for your input...

Steve