Haynes/Chilton suck. I've got a ton of factory service manuals from a dozen different auto manufacturers and I've yet to come across one which is as poorly written as those two companies' offerings.
I posted a better means of testing the VAFM than what is specified in the Haynes/Chilton and TSRM just the other day:
http://www.toyota-supra.info/forums/101981-post10.html You still need to test the FC switch (VERY important to pay attention to as it's a complete cutout switch) and the temp sensor as prescribed in the TSRM. The FC switch or its wiring is another possibility.
The load specific behavior of the failure isn't decidedly characteristic of a faulty EFI Relay or Circuit Opening Relay but they're simple enough to test and their failure may cause intermittent cut offs.
I don't recall you mentioning having tested them yet, but test the 100A fusible link (the old wire type used in earlier models will eventually corrode to the point of becoming a crippling restriction in the electrical system) and test the relay and resistor pack for the fuel pump.