a/c pressure readings question

Hi, I replaced the a/c compressor in my 2001 Impala (no dual climate control) last year because it sounded like a hail storm when it was running. Prior to that, the air worked great and had for the past 4 years that I owned it. When replacing the compressor, I also replaced the filter and drier, as many threads indicated would be a good idea. I dumped out and measured all the oil in the compressor (read, don't have an evacuator) and the drier and dumped that much new oil with dye back in the system. I hooked up my vacuum pump up and ran it for twenty minutes, and let it sit for half hour and the gauge never dropped one pound. So, I refilled it with 134a, as closely as I could get to the correct poundage (using a keg and gauges), and it worked pretty well, for about 2 weeks, then the compressor wouldn't engage anymore. I looked for dye leakage and could find nothing. She finally got sick of no air, so I recharged it a little and added a little more dye yesterday and ran it for 20 minutes, again no sign of leakage, but the driver's side was blowing 55ish and the passenger side was 40ish. I assumed it was a little low, as the pressure was 22 and 150. So I added more 134a this morning and now both sides are blowing around 30 degrees (outside temp is 75). Here are the readings on at idle and 2000 rpms.
Idle 31 & 175 2000K 27 & 190

Does that look right? I'm doing my best to learn a/c service, as that's really the only area I'm not confident in. Sorry for the long post, but any help would be appreciated. I don't want to keep filling up the system every 3 weeks.