2000 windstar 3.8l SEL Transmission as if O/D not engaging
I am having a weird problem and I don't know if my transmission needs replacing.
When my van is cool, (hasn't run for a few hours) and I drive at 120 km/h (65mph) my rpm reads a bit more the 2000 rpm. After about 20-30 mins of driving it is as if my over drive gets kicked out and I jump to about 3000 rpm.
The funny thing is my OD light doesn't flash, and when I push the O/D button I get an RPM surge (perhaps 100rpm more then is settles back down). When the tranny is working correctly, 2000 rpm, and I hit the OD button, the rpm goes up the 3000 rpm, when I push the OD button again, it revs back down.
SOOOO, the tranny seems ok. The tranny fluid doesn't smell burnt, and is clear of any particles. Ford says its the tranny but there are not error codes. I don't believe them since the tranny works when I first start the van. I don't have any unusual clunking, I can change gears properly...etc
I simply don't understand the issue.
One thing I have noticed is when I press on the accelerator I hear a hissing sound as if a vacuum line is leaking. If I were to guess where the hissing is coming from, it it coming from behind the plenum cover. (I did the error code 171-174 cleaning/mod last year and changed the sensor for the P401 code). I mentioned the hissing to Ford and they said it had nothing to do with the tranny and it wasn't a problem since there were no error codes.
Any help/suggestions would be much appreciated. I searched the forums and couldn't find anything that resembled this. The only O/D problem I say were when the OD light was flashing on and off, but my van doesn't have that issue and all the gears work.
Thanks in advance!!!