A couple problems after head gasket replacement (long)

After completing a head gasket replacement on my '01 2.7, the engine is running fine, all the internals seem great. However I have a couple issues that all might be related or not.

1. High idle - Engine races to near 2k rpm. I've cleaned the MAF and throttle body. Checked and re-checked the vac hose connections. Sprayed throttle body cleaner to find intake leaks. Checked throttle cables, in fact the throttle valve(?) appears closed all the way, can't turn it closed. Now after cleaning the MAF I forgot to plug it back in, started truck (CEL codes) but the idle was almost right, 1200 cold. Plugged in and shot straight up! Also, while spraying for vac leaks for the 3rd time or so, I popped a p1135 code. Now I'm seeing that this is a front o2 sensor, but it is about 6 months old and hasn't been a problem. Could the o2 sensor have gotten gunked up during the first run smoke out after the rebuild? Could this sensor be my problem? I'm getting no other CELs. -- [UPDATE] I cleaned took off the throttle body and cleaned thoroughly. I also removed and cleaned the IAC. After reinstalling, the High Idle problem is gone. With that said, I'm still getting the p1135 code. Seems I will have to investigate this further.

2. Spiking temp gauge - Occasionally the temp gauge spikes to redline, sometimes the engine seems to "miss" about this time, sometimes the engine runs fine through the spikes. Will the computer try to kill the engine if the temp gauge pegs? I cleaned the sensor, when I had it disassembled, cleaned the connector with Wire Dryer, blown out the connections, made sure that the ground wire to the head is tight, replaced the ground wire to the battery. Is there another ground wire I'm missing? It seems like a grounding issue to me as the sensor only has one wire. Also, I have a scan gauge and am seeing an actual temp of 170-178 while the spikes are showing redline.

3. One exhaust nut won't thread - This one is a bonehead move on my part. I noted that this nut was cross-threaded when I took it off. When I had the head re-worked, I asked them to make sure the studs were all good and renew if needed. I asked again when I picked up, and they said the studs would be fine. I think they re-cut the threads on the problem stud, BUT I didn't bench test before installation. Now this stud won't come loose, it looks like it might be twisting the tip as if it's softening near the tip. This is even after soaking with WD40. I can't really get a dye on it as it's the rear bottom stud. HOWEVER, after maybe a total of 40 minutes run time, I don't hear or smell an exhaust leak. Maybe I'll take it back to the place I got the head done and have them fix it. But I include this just to disclose in case it might effect the idle issues I'm having.

Any help or insights on this would be helpful. Seems this project is almost complete, I would just like to close the hood on this one. TIA.