Q: I have a 2002 chevy avalanche z71 it won't move forward in any gear,but it will move in reverse

Check to see if any diagnostic trouble codes have been stored in both the PCM and TCM. Check the fuses in the circuits that power the transmission controls. Occasionally, a short in a sensor such as an oxygen sensor will take out the fuse and the transmission controls share that common fuse. Verify that when you shift, the external lever on the transmission that controls the manual valve actually moves into the drive position. Confirm exactly which gears work and which don’t work because that is critical in the diagnostic. For example, in addition to reverse working, if you can get ANY movement in L1 or L2, but still no movement in D, that points to a broken forward sprag. Check the fluid level and condition. Finally, you can use external gauges to test hydraulic pressures and see if they are in the required range when you shift to D. If pressure is normal, that means you have a broken mechanical part like a band. If pressure is low, there is a leak somewhere, a valve body fault, defective clutch piston, possibly a problem with the pump and so forth. There is a very good diagnostic book on this particular transmission - it is a really common unit - and tons of technical support for rebuilding. If none of the foregoing possibilities pan out, your two best options are to have a certified mechanic from YourMechanic diagnose it or, in lieu of that, work off the diagnostic book for the 4L60-E transmission, otherwise you’ll be wasting a lot of time guessing as there is a very specific decision tree that is used in diagnostics. If you desire that a specialist from YourMechanic diagnose the fault just request a failure to shift diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.