This is a friend of ours rig...

Runs great all winter, but as soon as the outside temp reaches 90, it starts dying after 40 to 45 minutes of driving. It has been well serviced, so I wouldn't think the fuel pump is an issue.

From past experiance, I'm leaning toward the fuel pump seezing up when it gets hot. Any other avenues to check out?

Update, a year later....

Replaced the fuel pump and no problem all winter. Doing it again, but seems to be altitude related starts crapping out a 4000', will restart after about 30 seconds. Replaced the mass airflow sensor, no dice..
What next?

TSB
98-26-2 FUEL - INFORMATION ON GASOLINE - TIPS TO RESOLVE VOLATILITY RELATED DRIVEABILITY CONCERNS

Publication Date: DECEMBER 18, 1998

FORD: 1985-1997 THUNDERBIRD
1986-1999 MUSTANG, TAURUS
1987-1999 ESCORT
1988-1994 TEMPO
1989-1997 PROBE
1990-1999 CROWN VICTORIA
1992-1993 FESTIVA
1995-1999 CONTOUR
LINCOLN-MERCURY: 1985-1997 COUGAR
1986-1992 MARK VII
1986-1999 SABLE
1987-1989 TRACER
1988-1994 TOPAZ
1988-1999 CONTINENTAL
1990-1999 GRAND MARQUIS, TOWN CAR
1991-1999 TRACER
1993-1998 MARK VIII
1995-1999 MYSTIQUE
1999 COUGAR
LIGHT TRUCK: 1986-1997 AEROSTAR
1987-1996 BRONCO
1989-1997 F SUPER DUTY, F-350
1989-1999 F-150, F-250 LD, RANGER
1991-1999 EXPLORER
1992-1999 ECONOLINE
1993-1999 VILLAGER
1995-1999 WINDSTAR
1997-1999 EXPEDITION, MOUNTAINEER
1998-1999 NAVIGATOR
1999 SUPER DUTY F SERIES
MEDIUM/HEAVY TRUCK: 1990-1997 F-700


This TSB article is being republished in its entirety to expand vehicle model coverage and revise the text.

ISSUE:
Some vehicles using winter blend fuels may exhibit a stall on start up and a no restart, hard start condition or a no start condition in unseasonably hot weather (greater than 27°C/80°F). These concerns may be related to fuel volatility from winter blend fuels during winter-spring and autumn-winter transitions and may result in a fuel pump vapor lock condition. This condition may appear to be a fuel pump failure but may be caused by winter blend fuel.

ACTION:
Refer to the following text for further information.

NOTE: FUEL TANK ADDITIVES WILL NOT RESOLVE THESE CONCERNS BECAUSE VAPOR FORMS FROM CAVITATION WITHIN THE FUEL PUMP. FILLING THE TANK TO FULL MAY BE EFFECTIVE. ADVISE CUSTOMER TO USE THE RECOMMENDED OCTANE GRADE PER OWNER MANUAL AND NOT A HIGHER GRADE.



Explain to the customer that this concern may be due to a low tank level of winter blend fuel combined with unseasonably warm weather. Advise customer that filling the fuel tank to full may be effective in resolving this concern. Also, advise customer to use the recommended octane grade per their Owner Manual and not a higher grade.


BACKGROUND

Gasolines are seasonally adjusted, meaning they have higher volatility (vaporize easier) in the winter and lower volatility in the summer. Government mandates to improve air quality have resulted in significant changes to gasolines, such as the mandatory use of oxygenates (ethanol, methyl tertiary butyl ether (MTBE), and others) in the winter or the reduction of Reid Vapor Pressure (RVP) in the summer. The addition of oxygenates (especially ethanol) increases volatility while the reduction of RVP reduces volatility.

Gasoline distribution practices often do not allow branded marketers to have much control over their gasoline's volatility other than RVP. Oxygenate (e.g., ethanol, MTBE) use is more dependent on local gasoline markets, rather than specific marketers practice. Therefore, it is difficult to recommend specific brands to avoid volatility related complaints.

Could be it, the tank level doesn't seem to make any difference though and there is no problem with start up it dies while traveling down the highway.
What would be the odds of them still running winter blend out here?