Small Aircraft
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 300; Flight Crew Total 22592; Flight Crew Type 450
Confusion; Workload; Time Pressure; Communication Breakdown
ATC Issue All Types
Human Factors; Procedure
When I fly from ZZZ to LGB; I file [route].  Everytime I fly this route; which has been probably 20 times so far; SOCAL always gives me an amendment while in very busy airspace.  They give me either a heading near RRIZE intersection to intercept V394 from POM VOR then V394-SLI-LGB or give me direct POM V394; which normally they don't.  It's normally the heading to intercept V394.  Sometimes they change my clearance many times before they settle on something.  I've already filed ATC's amendment; because I know they will give me the amendment; and ATC gives me what I normally file anyways at ZZZ; and then enroute; I always get this amended clearance with the heading to intercept a new airway (V394). When given this amended clearance; it couldn't happen at a worst time.  There is a lot of traffic in the area; they are usually giving me a descent clearance and it takes awhile to tune in this new clearance into the G1000 flight plan.  It's not a quick thing.  There's no way I can look out for traffic for up to 3-4 minutes.  My head is down for 3-4 minutes. It's very unsafe.  It happens everytime I make this trip.  I even advised ATC of the issue and it sounds like they know about it; but aren't doing anything about it; because it's been going on for 18 months now.Please help make this a safer route.
Pilot reported receiving amended clearance inflight repeatedly.