My Subaru Legacy while driving gives delay kicks,its a automatic transmission but what may cause it?

EASY and CHEAP FIX! I will bet MONEY you have been suing CHEAP OIL CHANGES like VALVOLINE or other WAX BASED oils, and NOW>>>you have a dirty IDLE AIR CONTROL VALVE and THROTTLE BODY from SLUDGE and TAR< and WAX deposits on them! The IDLE AIR CONTROL VALVE gets Signals from the computer and the O2 sensors to FINE TUNE the air/fuel mixture under acceleration and in STOP AND GO traffic!>>>get a can of AMSOIL POWER FAOM from a local AMSOIL dealer! Remove the intake AIR snorkel and clean BOTH SIDES of the exposed THROTTLE BODY plate and REMOVE or CLEAN the visible PORT HOLES inside the t body to access the IAC valve and **** will OOZE OUT! The SAD thing is that most people just do NOT GET that all cars made with special ENGIEN TECHNOLGOY REQUIRE the use of REAL SYNTHETIC OILS with proper SPEC NUMBERS! For a SUBARU i would be tempted to buy TOTAL ENERGY OIL for ASIAN cars, or use PENNZOIL TULRA PLATINUM that gives an AMZING 500,000 miles extended warranty with PROOF you changed the oil every SIX MONTHS to ONE FULL YEAR!>>>ALSO change your FUELFILTER as a clogged up one will affect TRANS SHIFTING as well! Install those MARVELOUS DENSO TIWN TIP IRIDIUM LASER spark plugs to get the MOST POWER and ECONOMY and OIL LIFE as it SAVE the converter from carbon build-up and keeps the O2 sensors CLEAN! >>ALSO SONMETHING WEIRD! The WIRING HAENESS to the transision is made with SOY shielding that RODENTS love to EAT! If AFTER you have cleaned up the IAC and T body and run the AMSOIL through the PCV valve to clean the RINGS to showroom  clean, and you STIL have this issue, GET A FULL TRANS FLUID CHANGE at the SUBIE dealership and NOT at most OIL CHANGE CENTERS that are TRAINED in the wrong way to believe that there is such a thing as UNIVERSAL FLUIDS and COOLANTS !THER IS NOT! The SUBIE dealer will have CLEAN equipment set up for SUBIE CARS ONLY! usign the RIGHT fluids and filter and cheap watered down VERSION of things! KEEP RECILTS if you are CLEVER enough to use PENNZOIL ULTRA EUO or ULTRA PLATINUM! It is made from NATURAL GAS and NOT from CRUDE OIL and continuously CLEANS the engine as you DRIVE IT and prevent many sensors failures and keep the converter tuned up for you as well! It s=is ALL ABOUT CLEAN and EFFICIENT here! VALVOLIN E should be OUF OF BUSINESS! Nearly ALL cars using it find their sensors getting corrupted and RUBBER getting DISSOLVED and SLUDGY TAR and WAX deposits in EVEYRTHING from the OIL PAN to the VALVE COVERS! A CLEAN engine will simply dissipate HEAT the best and RUN it's best>>>POWER WASH engine with GUNK ORANGE ORIGINAL ENGINE CLEANER at a DIY CAR WASH and clean the space BEHIND the radiator where LEAVES< FUZZ, FEATHERS, SEEDS< GRASS< and ANIMAL DROPPIGNS have collected! BYE for now!

Forget dishing out $100 to be hooked to machine.  Any good mechanic will tell you what it is by driving it for a few minutes.  Since that is not you, go see one.

Go to the dealer to have that diagnosed. Their factory scan tool can pull any transmission codes and read live transmission data while driving.

Transmission Control Solenoid 

Check transmission fluid. It may be low.  You get a mach to check it properly if you don't know how to check oil level.

Might have filthy dirty transmission fluid and a filthy filter