96 chevy 1500 van trans no second

i just receintly receive a van in my shop sith no second. trans fluid was just changed (by someone else)and thats when the problem started.

symptoms are:
first,third and O.D. are o.k.
1-2 and 2-4 elect. syl valves are new
no manual second, even on diag with road test
shift from 1st to 3rd at 20 off the peddal and at 30 on the peddal
good second clutch band (i know this because o.d. uses this band)
gasket is not covering syl passage

THIS IS DRIVING ME NUTS. i have had the pan off twice and checked everything accept a sticky valvebody which i will check tomorrow. i'm sure there is someone out there who has had this problem whereas it is prety common. ANYTHING, I WILL TAKE IT=ADVICE, OPINION, A BULLET TO THE HEAD...

read the others post im tring to fix mine till now with just a 50 percent solved im going to change the valve cluster to fix it completely

I took to the shop again the problem wasn't fixed at all, although it works fine its start to slipping after a short trip in the highway, with speed over 50mph, when arrive to a reduce speed area like stop sign its start again shifting abruptly from 1st to 2nd and 2nd to 3rd and when i speed up faster (i usually speed up very slowly trying to protect te gearbox) but when i speed up faster the abrupt shift seems to be softer and i think the computer show the same codes again, any help so far? thanks