1994 Toyota Pickup Hesitates and sputters at highway speeds

I have a 1994 Toyota 4x4 with a 22RE engine. A few months ago, the engine started hesitating and sputtering at highway speeds going up hill. As if it were starving for gas. I replaced the fuel filter at that time and it seemed to solve the problem. But the problem is back and it seems to be getting worse. I tend to think it is a problem with my fuel injectors. The engine starts up fine and runs well on level ground, but when I put a load on it, the engine starts to hesitate and sputter. The engine is getting old and it is probably time to replace the head gasket. If not the whole engine but I need to figure this problem out first. Given the price of new injectors I was planning on taking it to a repair shop to have the problem diagnosed hooking it up to a computer for the diagnosis. Am I right in thinking it is probably my fuel injectors? Any advice you could give me would be greatly appreciated and after that I would be happy to make a donation.