Hard to give a hard straight answer with the info given. Because you say GI bleed nothing else. But reading between the lines you find Tachycardia, Hypotension, and potential Hypovolemia. = decompensating shock = 12 lead. But I will say since it was not my call and I did not do the exam and HX on this Pt. 3 lead may have been appropriate. But with the info given fall on the side of treatment. Since you didn't say other wise I will assume this pt. survived the transport and no harm done due to 3 lead -vs- 12 lead. which would make this a great moment of influence, to train the medic on why a 12 lead was warranted. Instead of a ding it should be a negative turned into a positive.