I have a 2002 chevy silverado 1500 ls with 150k miles the code po300 came up and when I try to pass someone up it down shifts, but doesn't go much more faster. I changed the spark plugs, plug wires, fuel filter' and I ran some sea foam threw it. Nothing helps!!! Does anyone have any good ideas what can be wrong with it?

Leaking intake manifold (vacuum )

Codes don't mean a certain part just that a "system" has not passed an internal self test at least three times, this testing goes on all the time while you are driving looking for errors. Here is the info on the possible causes of this transmission related code. A common cause is failure to have the transmission fluid replaced at least every 60,000 miles or sooner if driving in severe conditions like dust and heavy loads
P0753 - Shift Solenoid A Electrical.
Possible causes - Faulty shift solenoid A valve
- Shift solenoid A valve harness or connectors
- Shift solenoid "A" valve circuit is open or shorted (located in the pan attached to the valve body.)
- Low transmission fluid level
- Dirty transmission fluid

Is there anyway you can pull a code? Because it can be solenoid related,for this type of transmission the speed sensor (VSS) is prone to do this,also how is the transmission fluid is it brownish or dark dark burnt , because if it is its a mechanical failure.I can pull a code if in T.O

have the fault codes read to find out the servo/solenoid that is not working'
check that the vacuum actuator for the transmission is working and that the vacuum hose is connected
that is the unit that makes ratio changes possible at certain rpms and vacuum settings from accelerator pedal positions

It is possible that the Transmission control module (TCM) has detected a problem with either the actual electronics in the ******, or that the TCM itself is bad. You should have the OBDll on the truck scanned and you'll know much more about what happened.

I did'nt know if you had a FLOOR SHIFT , COLUMN SHIFT EXPORT OR COLUMN SHIFT
So here is the most common....the COLUMN SHIFT....

it may be a bad tps ( throttle position sensor ). it causes transmission shift issues, bucking,jerking, idle surging, engine cut off, surge while crusing down highway. if this does not solve problem, it may be a sticking valve body in transmission. have a good day !! for an automatic tranny.

Start with a tune up, spark plugs, spark plug wires, fuel filter, air filter and that might cure the PO300B code, hope this helps, Gary

try changing the shifter cable or look at the transmission to see if the cable linkage is bent

you have to read out the codes. po300 is misfire detected. maybe a coil or injector. could also be intake leak