My transmission is not engaging correctly. Once engaged in drive it shifts fine. To get it to engage i must rev engine until about2500 rpms and it engages

Check your transmission fluid level. When the engine is not running the fluid is not being pushed into the torque converter so check the fluid level with the engine is running, from a safety point of view have a friend sit in the driver's seat with a foot on the brake with the transmission in park or neutral. If the level is low, extra fluid can be added via the transmission dipstick tube ( DO NOT confuse this with the dipstick for engine oil!). If the problem persists it could be that you have sheared the oil pump shaft within the transmission. What ever the cause there is little that can be done by way of DIY and a consultation with an auto transmission centre would be the best next point of call

On older subarus there is a shift filter on the fender well inside the engine compartment. Hoses run from the tranny and back. Change it.

Also, Please make sure you have the correct transmission fluid as specified by Subaru.