Working on a guys 1988 E350 motorhome. Says that after 40km or so on a warm day it loses all power and barely runs, he has to pull over for 15-20 mins then start off and do the same routine over again.

New TFI module (My Bronco II was having the same symptoms when its TFI went bad, no change with the 460 )
Fuel pressure 30 at idle, 35-40 when the throttle is tapped 20 when held at mid throttle in park. 40 at idle with fuel regulator vac unplugged, 40 when throttle tapped. 25 when held at mid throttle.
KOEO code 33
KOER code 21, 33

Any suggestions? I cant replicate the problem. When I drive it it works fine, never get a chance to drive it on a warm day. Might have to take it out and go fishing!