transmission problem on 1998 Chevrolet Lumina

My transmission is slipping when I put it in reverse and than when I put it in overdrive are any of the forward gears, but does fine at high speeds and low speeds after a few minutes, what can it be.It has a transmission code PO1870 to

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2 answers 2 comments
when was the last time it was serviced?? sounds like a seal issue but could be a partially clogged filter. if you have been driving for a while like this, damage may have been done internally.

Roy
I serviced it earlier this week and still having problems
A code P1870 usually indicates torque converter slippage. If you bring your car over to Mr. Transmission on I-10 East (713-455-1780)or on Antoine (713-683-0700), we will check it out for free and tell you what needs to be done.
ok Thanks