87 TBI Questions???

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Howzit Guys... I'm kinda new here and was hoping for some input... I have a 87 R10 5.7 with a TBI...

First off it idles perfect and temp stays cool but there is a problem... Once in a while when the truck is under load it'll just bog down (kinda like no gas) theres just nothing for a little bit... I let off the throttle and press it again and it's fine... Could you guys maybe give me some ideas of where to start? Could this be a gas or elec problem? I changed the fuel filter in front the tank already and dumped a can of sea foam in the tank... also used carb cleaner and blasted down the TBI (carb)... Anyone come across something this before??? EGR??? Vacum?

Oh there is one more thing it has lots of power when leaving a light (auto with a over drive) 1st and 2nd is ok but when it shifts higher it just lugs and no power unless I floor it to kick it back down.