As N2TRUX said, test the fuel pressure.
TBI systems do not have a fuel pressure test port.
The fuel pressure is tested by using fittings to tee in a pressure gauge. I like to tee in the pressure gauge where the fuel filter is located. If the pressure is good, both the pump and regulator are ok. If the pressure is low it could be the pump or the regulator. If the test is done with a method that allows the fuel filter to be in place, a dirty filter can also cause low pressure. The regulator is inside the TBI unit. Stopping the flow in the return line momentarily will test to see if a low pressure problem is caused by the regulator. A bad regulator can let the fuel return to the tank instead of maintaining the correct pressure. If pinching off the return line makes a low pressure reading surge above the specification pressure, then the regulator is the problem.
The TBI fuel pressure specification for small block Chevy’s is 9 – 13 PSI with the truck running.
Here are some web sites showing fuel pressure test equipment. The first tool gets installed where the fuel filter goes. Most people use the tool in the third site next to the TBI unit.
I you already have a pressure gauge like shown in the second web site below, all you need is the tool shown on the first web site. If not, the third would get the pressure tested for the least money.
http://www.sjdiscounttools.com/ta37650.html
http://www.actron.com/product_detail.php?pid=16174
http://www.actron.com/product_detail.php?pid=16175
http://www.cfm-tech.com/catalog/fuel...er_2940807.htm