What exactly is transmission slippage? I am not

It is usually a good idea to get it to a auto a mechanic if the transmissions begins shuddering, but there are some things you can check at home. If the vehicle shudders this may be a sign of low trans fluid or dirty burnt fluid.
Check the owner's manual for the location of the dipstick for the transmission pull a dipstick out and look at the fluid on the end of the dipstick if it's bright red its good if it's black or brown tis burnt you can smell it smell of burnt smell.
No idea of how many miles but if over 100k dont do a trans flush have a "trany splash" done. Flushes on high mile cars can change the fluid 100 % but not the filter. Splash changes fluid in the pan but not the torque converter. Unless there is a drain plug on converter, but a new filter will clean up the converter fluid.
Find a reputable mechanic so you dont end up with a bigger problem if its just the fluid.
Oh if when you pull the dipstick and you do do that and you see that the fluid is a little burnt or it's low always check tranny fluid when the engine is running
To get a accurate reading.

Transmission shuddering combined with transmission slippage may be a sign that too little (pluged filter) or too much fluid is making its way to the transmission. This is usually a telltale sign that the torque converter is failing.

Hope this helps a little.
Best of luck.

P0700 is the generic transmission code that the ECM uses when there is a transmission malfunction. No real common issues or causes, other than low fluid/component slippage detected.

There are many things that could conspire to rob mileage. My first thought was possible transmission slippage. Although your city rating is horrible, the highway mileage is just a little off. 23-25 hwy is correct, 23 for lousy doped California gas, and 25 elsewhere. My guess is that you have slippage but above 45 mph, you are still getting advantage once the converter lock takes effect in overdrive. Just slippage until you reach that lock point.
Start with a full diagnostic of all stored codes in the ODB II computer, both for the engine and the transmission, then an evaluation of your transmission from a good shop.
Good luck, the Equinox is a darned good car,and worth the effort.

I would change fluid and filter only do not do anything else,after market gasket is not so good.

your car is equiped with an input/turbine and an output/turbine sensor the purpose of the sensors is check for slippage in the automatic transmission if one of the sensors is not working then the onboard computer system will opreate in limp mode and turn on the check engine light or service engine soon light witch ever one your car has, but you will still be able to drive the car it just will not shift real well intill you get the sensor replaced.....good luck

Slippage on turns almost always means you are low on fluid.

Flush and filter rarely helps, but is always worth a try.
Remember that only less than a third of the fluid is in the pan, and the rest is in the torque converter, and can not be drained.

okay have you check the fluid level, they do sell transmission slippage fluids, the exact name eludes me. Hope this helps Tim

Thats it. another problem is you should feel a good positive shift, not just lazily shifting into gear. when driving on the road and the engine revs up but the car doesnt get any faster. The first thing to do is verify the trans fluid level.

it must be something to do with electronic control to gearbox ecu wireing i assume the replacement gearbox came with tourqe convertor a diagnostic check might be best option

reverse band is a goner