Ran and reached heart rate of 203 per report but at the end of the run watch auto set my max heart rate to 194?

If the watch detects and reports a lower max hr than the absolute maximum recorded, it would suggest that Garmin already implements some kind of filter to exclude erroneous hr glitches. So the question is whether you can do it better by eyeballing the hr graph. 

(I personally have switched off max hr detection and done a self-test to find out my max hr.)

9955610 said:

Should I adjust my max heart rate to 203 or leave it as is?

This value is the most important input to your watch, aside from good HR data capture with a strap and good pace/power capture.

I personally don't trust the HR Max detection at all, despite the improvement in filtering out outliers in the algorithm, and all the precautions I take to wear a chest strap correctly and inspect the data. Too many times, the watch has suggested an absurdly high HR Max.

I would disable the detection and run an HR Max lab or field test, if your doctor lets you. These tests rely on pattern of efforts that let you estimate your HR Max more accurately. You can also triangulate your HR Max through various estimations methods:

- run an all-out 5k race and add 4 to 5 bpm to your HR

- run the next anaerobic workout at maximal but steady pace and run the last interval at the same pace but until complete exhaustion. You should be we few bpm off your HR Max

- run sprints up-hill until exhaustion, same as above

- if you are well trained, take your LTHR and divide by 0.90. For less trained individuals, the value can be around 0.8 so your mileage will vary here.

- take the 220-age formula and adjust the HR Max up or down by a few bpm, run a few weeks and observe how your training effect, race predictions and workout suggestions goals behave. I used that method when I first got my Epix 2 and converged to a very good estimate over a few months, then confirmed with several types of field tests since then.

I agree with Etupes25. However, if you end up using just a formula to guess your max hr, be aware that the 220-age has been found to be quite inaccurate, there are better (but slightly more complicated) formulas, see for example marathonhandbook.com/.../ (that page also describes field tests).