Now that most vehicles are more electronic and less mechanical, good grounds and power connections are more important than ever. You just experienced one of those issues.
The ECU is attached to the chassis on a ground plane. I don't think Toyota relied on that attachment for a good ground. However, the three electrical connections to the ECU have many grounds. I suggest the mechanic put vasoline or electrical contact grease on the pins of all three connectors. Oxidized connections can cause the type of problems you have been suffering from on the runner. He may very well have lubed the pins and it started running just fine. Under hood ground points are critical. Battery ground is attached to engine block that is isolated with rubber mounts. The ground wire from the back of the block to the firewall is CRITICAL. I suggest you remove it, clean it and put it back on with vasoline under the attach points. And, I suggest whenever any electrical connector is removed, paint all those pins with vasoline. Works for me, including the battery!