Need help with refreshening

[72firebird]

Well I had a tranny built by Vince Janis a little over a year ago and have loved it. However I've always had problems with the converter staying locked, or unlocking after a highway cruise. I've only got a 9x11 3000 billet l/u stall converter and have a fairly large trans cooler and have it so it runs through the stock trans cooler, then to the B&M which is about half the size of my radiator (and sits in front of the radiator). So I've just kind of figured my problem has been my l/u solenoid in the tranny. Since it's been a while since I put the tranny in I figured I'd go change all the fluid and filter this week, and while I have it open I could check the solenoid. What do I need to look at to be able to see if it's bad? What's involved in replacing it? Also here's a list of what Vince installed and is there anything besides for getting the 700r4 filter that I should look at? Also, what is your opinion of what I got? What should it be capable of holding?

1-PTS billet foward drum
1-hardened pump stator
1-Alto 2 5/8 band
1-3200 gasket seal kit
6-red eagle frictions (3rd)
6-Kolene (?) heat treated steels
1-overdrive piston 3 frict.
1-.500 boost valve
1-heavier pressure spring
1-modified valve body & sep. plate V.J. specs
1-32502A roller clutch
1-700r4 filter element
1-washer kit
3-overdrive frictions
3-overdrive steels
1-direct drum clearanced
1-overrun clutch
1-4 B/W forward frict.
1-blue printed pump