A/C not producing sufficient cold air

[mrzzzr1]

Have replaced the Electronic HVAC Controller with one my mechanic found on the west coast. GM original not available any longer. (Original controller was erratic a/c delayed for a period and also cut in and out whenever it felt like).
Have done 2-3 rechages the first two with dye and no leak detected although the feon was down ~.2 lbs. after a couple weeks.
Converted the old R-12 with new R-134a to reduce freon rechage cost.

Mechanic says he has done everything he can. Says the only thing left is there may be a pin hole leak in the evaporator core and he can't, or doesn't want, to fix it.

Have run the a/c for a couple months since with not much change. When it is hot I max out the temp at 60 and the fan on high and it barely keeps up.

A/C only seems to run on "AUTO" setting (is this they way it is supposed to work). When I run the outside air though the system (upr and lwr vents) without a/c it still seems to produce a/c sometimes (another bad HVAC controller).

Any ideas or suggestions are appreciated.
I think I have spent way too much time and money chasing this one.