Seems normal in 1st & 2nd
First check trans. fluid. It should be full, & clean. Clean means light red color fluid (like red cool-aid) if it looks like darker red, or brown fluid, like motor oil, that is way too dirty & should be flushed. May need to change the filter too. dirty trans. fluid is your big enemy. could also be an electrical problem in the trans like a shift solenoid or something like that, but check for clean fluid first.
SOURCE: I have a 2003 GMC
Sure sounds like a slipping transmission to me. When is the last time you changed the transmission fluid? Before you go dumping $2,600 for a new transmission, I'd do a transmission fluid change first. If you do change the fluid, use Dextron 6, it's GM's new transmission fluid, much better than the fluid you have now. Not to scare you, but my transmission went out at about 100k miles, so you're doing good if it hasn't been rebuilt yet.
The
following are the general instructions on the start of diagnosing any
electronically controlled engine or transmission problem.
The
engine and the automatic transmission (transmission control is only
for automatics, engine is still computer controlled no matter the
transmission type) in this vehicle are computer controlled and in
most cases when a fault occurs a fault code is stored in the memory
of the computer control module. There are exception to this, such as
the Mass Airflow Meter and fuel pressure problems. What must be done
is to have all the basic testing done such as a scan of the system
for fault codes as well as a check with a live data scanner tool for
engine functions that are not within range of normal, a trained
technician is required to know what is correct and what isn't, then
based on careful diagnostics done from a factory repair manual the
correct part is replaced or the wiring repaired or the computer
replaced (known as the PCM), which is very rarely the problem. Other
basic checks must be done as well such as mechanical problems with
the engine as well as engine state of tune and mileage on the engine.
The transmission can have mechanical issues as well such as no gear
engagement at all or a failed pump or other pressure related
problems. Also engine mechanical problems ca cause many
drive-ability related problem such as rough idle and other symptoms
The
engine and the automatic transmission (transmission control is only
for automatics, engine is still computer controlled no matter the
transmission type) in this vehicle are computer controlled and in
most cases when a fault occurs a fault code is stored in the memory
of the computer control module. There are exception to this, such as
the Mass Airflow Meter and fuel pressure problems. What must be done
is to have all the basic testing done such as a scan of the system
for fault codes as well as a check with a live data scanner tool for
engine functions that are not within range of normal, a trained
technician is required to know what is correct and what isn't, then
based on careful diagnostics done from a factory repair manual the
correct part is replaced or the wiring repaired or the computer
replaced (known as the PCM), which is very rarely the problem. Other
basic checks must be done as well such as mechanical problems with
the engine as well as engine state of tune and mileage on the engine.
The transmission can have mechanical issues as well such as no gear
engagement at all or a failed pump or other pressure related
problems.
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