1999 Dodge Caravan Transmission Connected to a Fuel Pump?

I had the engine and transmission replaced 3 months ago. Refurbished equipment. Recently on the freeway, driving was fine until we slowed for traffic. Then the transmission would not shift - to safely get off freeway RPMs were 4500 at 50mph. I drove home using surface streets. By then the transmission was shifting okay again. I turned van over to mechanic for evaluation. They reported the shifting was fine but was connected to low pressure in the fuel pump. Huh? Thnis cost $650 to replace. When I picked it up, a second mechanic said the two were not related. Was I ripped off? Being non mechanical feel like a fool.