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So swapped a yank 3600 in and added a 3.42 diff. Filled fluid drove fine then during a long let break in drive trans started to slip. Put it back on lift, fluid low topped it off runs great not slipping that I can tell. Working on the tune car shifts quick and smooth but at 70 mph cruise it wants to hold 2900 rpm’s and will occasionally drop to 24/500 rpm’s. When I jump on it from a 40 roll it will drop a gear and haul but then bang off the rev limiter and never upshift. If you slow walk it to WOT it will not go above 105 and seems like it’s either not up shifting or the slipping wrecked it. But when I manually upshift while driving it does t feel like it’s slipping and will shift through all the gears fast and firm. At a total loss here. Anyone have any ideas? Thanks.
I have a 3.73 gear. My car holds about 2400 RPM in overdrive at 70mph and I’m running a 26.1 inch tire. Tire size makes a difference.
sounds like your tune is way off and/or you lost overdrive gear if it’s holding 2900 RPM at 70mph. You need to take it to a professional and have them look everything over.
Key here is what Feeder82 and Beast are saying. If you took the car for a drive BEFORE tuning, youve probably damaged the trans to a degree. To what degree, nobody knows. A true knowledgeable professional tune cant be overemphasized here! I speak from experience; my 4L60E has almost 150,000 miles on it, with over half those miles spent behind 2 different 600hp 427s. It has never been apart. I installed a Yank 3,200 at around 50,000 miles, installed at the same shop that did the tune. At 60,000 miles, the first 427 went in. The only thing I've ever done is change the fluid and filter (myself) at 100,000 miles. Trans is totally stock, unless you count the Yank. I am definitely in the minority, but I'm also definitely proof that a 4L60E can go a long way IF properly tuned. Best of luck....