Hello, new user here. I guess I'll start with a short bit about myself in the event that I may be of help to someone else one day. I have had a wrench in my hand for right at 30 years. Started out working on cars and light trucks. ASE and GM certified although these certs have expired. Now working on heavy trucks and certified currently. I have two issues with my Suburban that I have been unable to isolate, and these two issues have irritated me for 3 years! 225,000 miles and in great shape although all original driveline. I'm hoping someone here has dealt with these issues! At highway speeds, transmission will hunt in and out of the "lock-up" feature of the torque converter. This only occurs while driving in the rain. Dry weather it works beautifully. Also at highway speeds regardless of the weather the engine will randomly and intermittently surge as though the key were turned off and then right back on again really fast. There is no backfire, no smoke, no loss of performance and no service engine soon light. No codes stored in the memory either. During this time, I have done the following: tune-up including fuel filter, cap, rotor, wires, plugs, ignition module, ignition coil. Fuel pump failed so it got a new one. Fuel pressure is at spec. I am stumped and so are my friends who are also many of them mechanics. I am thinking ECM? What are your thoughts?
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