If you feel fitter and are faster then that is what matters. But here are a few specific things to consider: Forget the maxVO2 numbers from these watches. They are based on some general algorithm and have no way of actually knowing what you VO2 is. Its takes a gas exchange test to tell this. If you really want to know (and why would you care?) then go to a lab and get tested. But forget the watch maxVO2. Many people report this exact same thing.
Regarding TP metrics: Have you set your zones based one some actual testing. Or are you guessing. Based on the TSS scores you quote I can say pretty pretty assuredly that something is way off. What TSS are you using? rTSS or hrTSS. Running in the aerobic realm (below AeT) will typically net a hrTSS of 55-65 per hour. So a 1.5 hour aerobic run on flat ground will give you a hrTSS of 90 not the 245 you were seeing. A TSS=245 workout is a VERY taxing workout.
Have you changed HR monitor? Do you use a wrist monitor (terribly inaccurate) or a chest strap?
So that covers the data side of things. You could be experiencing some actual physiological reason for you needing to run 30-60 sec/mile slower to stay at 135HR. The first thing I would guess is fatigue. If you have been consistent in your training and careful not to do too many harder workouts, you should see improving pace in the aerobic zones. If not, it is more likely related to too much or too hard training not too little.
Other possible causes could be related to illness or nutrition or poor recovery.
Let me know if any of this helps.