Why is my Evo X SST transmission slipping or shifting late?

Short answer: Check the fluid first. The SST needs its own fluid, and ATF can make it slip. On tuned cars, extra torque and the tune can cause slip on the 1-2 shift. A short occasional delay with firm shifts is usually not a problem.

Symptom: Revs flare between gears, the car bucks or slips at low RPM, or one or two shifts per drive feel delayed.

What to check first

1. Confirm the SST has the correct fluid and a recent fluid and filter change.
2. Note when it slips (gear, RPM, warm or cold).
3. If the car is tuned, have the tuner check the ECU and TCU settings.
4. Read transmission codes with a scanner that can see the TCU.
5. Get a specialist to check clutch wear before replacing the transmission.

Likely causes

1. Wrong transmission fluid. The SST is a twin clutch automatic and needs its own special fluid. Regular ATF can make it slip. One owner found the previous owner used ATF.
2. Worn clutch packs. The SST has wet clutches inside. They wear, especially with more power than stock.
3. Tuning and clutch pressure. Owners say a good engine tune matters, and some raise clutch pressure through the transmission computer (TCU) to firm up shifts.

What it usually costs

Owners in these threads didn't post prices.

Is it safe to keep driving?

Mild delays are OK to drive on. If it slips and flares under power, get it checked, because slipping wears the clutches fast.

DIY or shop?

Fluid service is possible for experienced DIYers. Clutch and TCU work is for a specialist.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists 10 recall(s) for the Mitsubishi Lancer Evolution in these years, and none is for this problem. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 39 keyword-matched complaints for Mitsubishi Lancer Evolution 2008–2015 (of 240 unique complaints queried, NHTSA complaints API by model year, queried 2026-11-05; keywords: transmission, sst, clutch, shudder, slip, shift, gear). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In EVO X MR SST issues on Reddit r/MitsubishiEvolution, an Evo X MR owner found the previous owner had used ATF instead of the SST fluid. After a fluid and filter change it still slipped sometimes, revving to 6,000 rpm, and new clutches didn't fix it either. He sold the car without finding the cause, and another owner said the same was happening to him.
• In Clutch slip EVO X MR on Reddit r/MitsubishiEvolution, a tuned Evo X MR owner at about 400 hp felt an occasional delay on one or two shifts per drive. Replies said slip below about 2,200-3,000 rpm on the 1-2 shift is common with added torque, that a good tune matters more than just adding clutch pressure, and that a short delay with firm shifts is usually OK.

Quick tip

Start with the fluid and the tune before buying clutches.

Vehicle focus: Mitsubishi Lancer Evolution X with the SST twin clutch (GSR/MR/SE), 2008-2015.

Safety / mechanic note

A transmission that slips when you accelerate can surprise you in traffic. Verify with a mechanic.