Try using a pressure regulator instead of a blow-off valve. You may have to set the pressure at a lower level than the blow-off valve is set for. Some trucks apparently defuel at high boost levels, some do not, depends on PCM programming and year. Yours may be one that does. Setting a overboost CEL or condition in the PCM generally occurs around 22-24 psi. With the big injectors, your blow-off valve may not be responding fast enough to avoid defueling. Using an adjustable pressure regulator will allow you to set the regulated pressure lower than 22 psi so it will respond fast enough to prevent the MAP sensor (and the PCM) from seeing overshoot pressures above the 22-24 psi range. Should not have to go below much below 18 psi though if at all. just experiment by setting the regulator pressure lower and lower until the fuel cutoff disappears.
You should post performance questions in the 94-97 mods forum for more responses.