Is it the fuel pump?

My 98 Toyota Sienna has had some problems that lead me to believe the fuel pump needs replacing. But I’m no mechanic; and I don’t trust any around here. Here are the symptoms: (1) check engine light starts blinking on highway when car’s going at higher speed and needs power to go up a hill at 3500 or 4000 rpms (the light has since remained on); (2) a few times (only occasionally) the car has refused to accelerate from a stop until a few seconds pass despite the gas pedal being depressed; (3) after sitting overnight, the engine takes a little bit longer (second or two) to start; (4) after sitting overnight, the engine runs rough for a minute or two (as though it needs a new plug), but then runs smoothly after the minute. Not sure if it’s relevant, but we had to replace a fuel injector recently.

I don’t think your going to hit right on the problem without doing some tests. Fuel pressure then scope (or multimeter) that throttle switch then after its running a engine manifold vacuum test. Almost forgot get that blinking light read and don’t drive it unless you absolutely have to until you see what failure is so severe that the light blinks.

Old, dirty, original fuel filter? Worn out spark plugs? Ignition (spark production)? Leaking fuel injector (fuel pressure static leakdown)?

If the CEL is on you must have the codes read. This will give some indication as to where the problem lies.

A fuel pressure test will tell you the condition of the pump.

Why is it you don’t trust any of the mechanics in your area? How are you going to get the vehicle repaired if you don’t take it to a mechanic?

check engine light starts blinking on highway when car’s going at higher speed and needs power to go up a hill at 3500 or 4000 rpms (the light has since remained on)

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P1234) not just their translation into English and post it back here.