My 1999 Chevy Suburban is stuck in LIMP mode. the truck first started to where it would seem to good but once it go to about 20/25 mph it wouldn't shift into a higher gear. I borrowed a simple code reader (dont know the brand off hand) and it gave me P0756. Looked up the code online and found references to the Shift solenoids A & B. I found a post online (Part 1 -Shift Solenoid A and B Tests. P0700, P0751, P0753, P0756 (GM 4.3L, 5.0L, 5.7L)). Did the test on the Solenoids, they were in fact bad. I ordered new ones and installed them, put everything else back. At this time, I put back the old trans fluid and replaced the trans pan gasket. Still no luck. I then cleared the code with the code reader and also unplugged the battery to clear anything else. Still no luck.

So here I am still stuck in LIMP mode. I have Read a few things this past week. One of which was to change the Filter and trans fluid (which I did), and or Check the Vehicle Speed Sensor (http://www.freeautomechanic.com/vss-...ed-sensor.html). Looked for it but dont know if I found the right item, because I couldn't find anything that looked like the image in the link. I however did find a sensor that looked like this (Gmc Suburban Speed Sensor | Racepages.com) and did a test with the volt meter and tested it based on the link from freeautomechanic and it tested good (about 200; the article says between 190 to 250 ohms).

So, now I am back at the same problem it is stuck in 2nd gear (LIMP Mode). I checked all the fuses I could today, all including the battery fuse, ECM fuses. I even disconnected the battery (both posts) and removed any battery fuses and ECM fuses for a good 2 hours. still nothing, however, it does seem like there is a difference in the shift to get up to and past 2nd gear. It seems like it shifts ok but I do believe it is only in 2nd gear. I've also shifted between all of the gears and I don't notice any difference. One thing I might add is that when shifting from Drive to Reverse or Park it wants to "stall", but only if you come to a stop quickly and then very quickly change to Reverse or Park.

Any and all thoughts are welcomed. I am stumped and cannot think of what else to try.

 

@cfreiling - that sucks!
I changed out the high pressure power steering hose on a Seville STS
The wiring for the sensor that screws into the knuckle on the hose has a long harness and has to be tucked and zip tied, or else it hangs down on the constant velocity of the front wheel drive. Eventually, it wears the plastic sheath on the wires, causing a short. Why do I mention this?
The same circuit that supports the tranny services the sensor for the Hi-pressure PS hose on chevy vehicles.
Panic ensued - the caddy defensively went to LIMP mode, too. Caddy trannys are known to blast at 120K and I'm at 280K
The dealer finally discovered the short, wrapped up the wires and I'm good.
You've checked all the fuses, I read. This fuse is in the box on the passenger fender and is marked -

 

Is this box inside the engine compartment?

Would you be able to tell me more about the wires?

 

@cfreiling
Its the fuse marked "IGN-1" on the passenger fender under the hood.

The pair of wires run to the sensor screwed in the knuckle of the high pressure PS hose on the Caddie STS.
Apparently, this circuit powers more items, too. One other may be your culprit.

Got my fingers crossed