Fuel GTH24V52LS Runs wide open 15 minutes acts like starving for Fuel.

My Husk acts like it is starving for fuel after 15 minutes running wide open on uneven terrain. I took it to the dealership where I purchased it, after doing the obvious, spark plugs, air cleaner, oil and filter, gas filter. Mr. Husk ran the mower and it did the running out of gas thing after 15 minutes. Mr. Husk replaced fuel pump, gas cap, Gas filter?? He said the NAPA filter was suspicious and replaced it with Husk filter. Mr. Husk said he blew out the fuel line and it did have some kind of restriction. Mr. Husk ran mower on level ground for 40 minutes and never bogged. I paid bill , took it home started cutting after 15 minutes , you guessed it, yes it started bogging and I had to choke the engine to keep it running to get it back to garage. I called Mr. Husk he said the next step is to pull gas tank, pour fuel into white bucket and look for whatever. I will be doing this today myself. Is there anything else that would make the engine be fuel starved after 15 minutes running wide open on uneven terrain? Thanks for any info.