Now that you mention another shop replacing the expansion valve but skipping out on the receiver/dryer there is a new concern. Every single time the A/C system is opened to atmosphere, moisture (water) enters the system. The only way to remove the moisture is to boil (evacuate) it out with a vacuum pump, holding a deep vacuum for 30 minutes or more. Any moisture left in the system is absorbed by the receiver/dryer and the only sure way to start with an "empty" dryer is to install a new one as the last step before sealing and evacuating the system. If the shop did not replace the dryer, I would question whether they evacuated the system before recharging with refrigerant. If they did not evacuate it, they also left air in the system. The interesting thing about air in the system is that it will lead to higher than normal pressures!
This is almost certainly what happened (no evacuation or poor evacuation). Drier desiccant is saturated and at some point will break down and travel to his new TXV where it will clog the screen.
I have no doubt there is both air and moisture in the system.
OP has a 'roll the dice' situation on his hands. If he wants to clean parts, check for leaks and replace only what appears to be faulty, this can be done. But on an old system (and a person meaning to keep the vehicle) it is often best to just go through the system and be done with it.
Assuming the Compressor is good....then New Condenser, New Evaporator, New TXV, New DRIER, new Schrader valves. Flush all the hard lines and replace all O-rings using Nylog on the O-rings, mating surfaces and Schrader valve threads.
Pump the system down (using a REAL vacuum pump) check for leaks. IF no leaks are found then continue to pull a DEEP vacuum on the system for a full 2 hours (this is where shops get in a hurry).
Then recharge the system (now empty, clean and dry) with a 'weighed in' refrigerant/oil amount. This will get you in the ball park....and then you can 'fine tune' the charge to get those last few degrees of vent temps by using the gauges and watching the vent temps (adding or removing refrigerant). This is also something shops don't do.
Gentlemen.....A/C work is no fun (no way around it). It can be expensive and time consuming, so do you really want to do it twice or three times?
IF it can be avoided please do not use dyes or sealants unless you are just destitute and have to have semi cool air.
Those who live in hot climates and depend on their A/C 8-9 months out the year.....would be best served by refurbishing the SYSTEM even it that means collecting the parts before hand.
I understand financial constraints can dictate what a person is able to do and I am not suggesting that in every case the entire system needs replacement.
IF you have a system that is currently holding pressure.....then careful evaluation of any problems is the thing to do (to a point).
In the OP's case.....he has slightly higher than normal pressures (depending on the ambient temp at the time). There are several reasons this could happen. Insufficient air flow, dirty condenser and evaporator, air and moisture in the system and a saturated drier are almost a certainty in his case. We also have no idea the refrigerant charge or oil charge.
A good shop with the proper equipment and a 'tech' willing to take the time to evaluate the system could fix it with a minimum of parts being replaced, but good luck finding one of those.
A DIYer without much (if any equipment) and little understanding of how an A/C works faces a daunting task. It's not Black Magic and folks can learn (I encourage that), but try to avoid having to do things multiple times and don't cut corners when it comes to A/C work.