'00 Sonoma 4L60E, no 3rd & OD

Ok, I'm tired of reading trying to find an answer to this question....

Looked at a 2000 Sonoma 4x4 auto. The truck had been sitting for a year only being driven a few times. It made a 350 mile trip (after adding a bit of tranny fluid) to it's current location and worked fine. Been sitting for sale since July.
Took it for a test drive and it won't shift out of 1st gear on it's own. Manually shift into 2nd and it will go into 2nd, but any other position drops it back to 1st. Reverse is fine.
REading other posts has me thinking electrical connection issue, but it's a shot in the dark. ANYONE??????

Is the fluid level good now.
What is leaking?
Was it ran low on fluid?
It needs to be put on a transmission capable scanner to see what is going on.
If any codes post back codes?

Ok, finally got a computer scanner on the truck. The ONLY code kicked back was low voltage-speed sensor. PO502. It make sense, but I would like someone to weigh in on this. So the question of the hour is.....

Would a faulty speed sensor cause the tranny to not shift?

Yes, but once the code is set the trans should default to a limp mode and shift based upon RPM and TPS, albeit very harshly due to the full line pressure. It might also shift at a higher than normal RPM.

I'm very familiar with the limp mode SLAM to second gear on the 4L60. This truck is definitely NOT going into limp mode.

Anyone else want to weigh in on this?

Blue Bowtie
Has summed it up.
You need to repair the code 502 to get it to shift right.
Go threw code 502 the repair flow chart.
Check speed sensor output and wiring.

A good factory repair manual or a all data sub has the repair flow charts.
http://www.alldata.com/products/diy/index.html

Is the dash speed ometer droping out?
Did you clear code and see if it comes back?
Any other codes stored in history?
Was there any freeze frames stored?

Possibilities are:

The boost valve/ PR valve is leaking from the end where the torque signal hydraulic line balances the spool;

The pressure control solenoid is functioning electrically, but sticking mechanically;

The actuator feed limit spool is sticking or its return spring is broken or missing;

Low/Reverse input clutch possibly sticking (I've seen that with a stuck apply piston):

http://mysite.verizon.net/strey/files/4L60OverRunForwardPistons.jpg

The 1-2 accumulator check ball is damaged or missing (fell through the plate);

The 2-3 shift valve spool or shuttle valve spool is sticking at the "2" position (there is no spring behind the shuttle spool);

Leaking separator plate.