No passing gear!

My father has a 97 Astro Van, Last few days we have noticed when the van is kicked down to pass, the van sticks in passing gear and will not shift. Continues to run in high RPM and will only shift until you let off the gas, needles to say, its worthless at this point. Another thing, A few days it was doing the same but when it did shift, it was like it threw ya forward (launch). The check engine light came on yesterday. We would like to check the computer for the code, but we are not sure which post to ground. The systems post are different then my 91 chevy. Can any one help?
Thanks in advance.

P.S.

The system is OBD II, I was told to ground A and B ( #5-#6 ) But #6 was empty. Tried #4 and #5 but got nothing :disappoin

Well since it's ODB-II you will need a code scanner to get the code. Jumping the pins won't work on anything other than ODB-I GM cars.

Autozone or Advance Auto should be able to scan it and get you the code. Sounds like a solenoid or something is sticking in the trans, forcing it to hold the lower gear.

Thanks for the info,
I'll check into picking up a scanner.